I'm getting this same crashing issue, but the backtrace does not match that of bug 6522. It seems to happen to me on inserting a float, but not always. Here is my backtrace:

Program received signal SIGSEGV, Segmentation fault.
0x0819c641 in lyx::TextMetrics::cursorY (this=0x8c5f91c, sl=..., 
    boundary=false) at ../../src/TextMetrics.cpp:1776
1776	../../src/TextMetrics.cpp: No such file or directory.
	in ../../src/TextMetrics.cpp
(gdb) bt
#0  0x0819c641 in lyx::TextMetrics::cursorY (this=0x8c5f91c, sl=..., 
    boundary=false) at ../../src/TextMetrics.cpp:1776
#1  0x08339635 in lyx::InsetText::cursorPos (this=0x8c5d478, bv=..., sl=..., 
    boundary=false, x=@0xbfffc28c, y=@0xbfffc288)
    at ../../src/insets/InsetText.cpp:364
#2  0x082b16c9 in lyx::InsetCollapsable::cursorPos (this=0x8c5d478, bv=..., 
    sl=..., boundary=<value optimized out>, x=@0xbfffc28c, y=@0xbfffc288)
    at ../../src/insets/InsetCollapsable.cpp:415
#3  0x081cbd81 in lyx::BufferView::coordOffset (this=0x8b4a150, dit=..., 
    boundary=false) at ../../src/BufferView.cpp:2210
#4  0x081cca66 in lyx::BufferView::getPos (this=0x8b4a150, dit=..., 
    boundary=16) at ../../src/BufferView.cpp:2294
#5  0x081ccb36 in lyx::BufferView::cursorPosAndHeight (this=0x8b4a150, p=..., 
    h=@0xbfffc3bc) at ../../src/BufferView.cpp:2317
#6  0x0838f802 in lyx::frontend::GuiWorkArea::showCursor (this=0x8b47ec8)
    at ../../../../src/frontends/qt4/GuiWorkArea.cpp:531
#7  0x08390212 in lyx::frontend::GuiWorkArea::startBlinkingCursor (
    this=0x8b47ec8) at ../../../../src/frontends/qt4/GuiWorkArea.cpp:367
#8  0x08390288 in lyx::frontend::GuiWorkArea::focusInEvent (this=0x8b47ec8, 
    e=0xbfffcad0) at ../../../../src/frontends/qt4/GuiWorkArea.cpp:674
#9  0x00470901 in QWidget::event(QEvent*) () from /usr/lib/libQtGui.so.4
#10 0x0086cfd3 in QFrame::event(QEvent*) () from /usr/lib/libQtGui.so.4
#11 0x00907d97 in QAbstractScrollArea::event(QEvent*) ()
---Type <return> to continue, or q <return> to quit---
   from /usr/lib/libQtGui.so.4
#12 0x0838f53f in lyx::frontend::GuiWorkArea::event (this=0x8b47ec8, 
    e=0xbfffcad0) at ../../../../src/frontends/qt4/GuiWorkArea.cpp:625
#13 0x004124dc in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /usr/lib/libQtGui.so.4
#14 0x004190f9 in QApplication::notify(QObject*, QEvent*) ()
   from /usr/lib/libQtGui.so.4
#15 0x08359008 in lyx::frontend::GuiApplication::notify (this=0x86fe390, 
    receiver=0x8b47ec8, event=0xbfffcad0)
    at ../../../../src/frontends/qt4/GuiApplication.cpp:1287
#16 0x00ec1a3b in QCoreApplication::notifyInternal(QObject*, QEvent*) ()
   from /usr/lib/libQtCore.so.4
#17 0x0042193e in QCoreApplication::sendEvent(QObject*, QEvent*) ()
   from /usr/lib/libQtGui.so.4
#18 0x00417db6 in QApplicationPrivate::setFocusWidget(QWidget*, Qt::FocusReason) () from /usr/lib/libQtGui.so.4
#19 0x0046b705 in QWidget::setFocus(Qt::FocusReason) ()
   from /usr/lib/libQtGui.so.4
#20 0x0837592f in QWidget::setFocus (this=0x8933e70)
    at /usr/include/qt4/QtGui/qwidget.h:416
#21 lyx::frontend::GuiView::setFocus (this=0x8933e70)
    at ../../../../src/frontends/qt4/GuiView.cpp:504
#22 0x08500e6f in lyx::frontend::TocWidget::on_typeCO_currentIndexChanged (
---Type <return> to continue, or q <return> to quit---
    this=0x8a32a90, index=-1)
    at ../../../../src/frontends/qt4/TocWidget.cpp:175
#23 0x0850101c in lyx::frontend::TocWidget::qt_metacall (this=0x8a32a90, 
    _c=QMetaObject::InvokeMetaMethod, _id=36, _a=0xbfffcce8)
    at ./TocWidget_moc.cpp:106
#24 0x00ec6c9a in QMetaObject::metacall(QObject*, QMetaObject::Call, int, void**) () from /usr/lib/libQtCore.so.4
#25 0x00ed53d5 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/libQtCore.so.4
#26 0x00836493 in QComboBox::currentIndexChanged(int) ()
   from /usr/lib/libQtGui.so.4
#27 0x008380ca in ?? () from /usr/lib/libQtGui.so.4
#28 0x0083bb01 in ?? () from /usr/lib/libQtGui.so.4
#29 0x008411f3 in QComboBox::qt_metacall(QMetaObject::Call, int, void**) ()
   from /usr/lib/libQtGui.so.4
#30 0x00ec6c9a in QMetaObject::metacall(QObject*, QMetaObject::Call, int, void**) () from /usr/lib/libQtCore.so.4
#31 0x00ed53d5 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/libQtCore.so.4
#32 0x00f259b7 in QAbstractItemModel::modelReset() ()
   from /usr/lib/libQtCore.so.4
#33 0x00ebc839 in QAbstractItemModel::endResetModel() ()
   from /usr/lib/libQtCore.so.4
---Type <return> to continue, or q <return> to quit---
#34 0x00a4be85 in ?? () from /usr/lib/libQtGui.so.4
#35 0x00a4dec6 in QSortFilterProxyModel::qt_metacall(QMetaObject::Call, int, void**) () from /usr/lib/libQtGui.so.4
#36 0x00ec6c9a in QMetaObject::metacall(QObject*, QMetaObject::Call, int, void**) () from /usr/lib/libQtCore.so.4
#37 0x00ed53d5 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/libQtCore.so.4
#38 0x00f259b7 in QAbstractItemModel::modelReset() ()
   from /usr/lib/libQtCore.so.4
#39 0x00ebca21 in QAbstractItemModel::reset() () from /usr/lib/libQtCore.so.4
#40 0x083b77f6 in lyx::frontend::TocTypeModel::reset (this=0x895ec54, 
    bv=0x8b4a150) at ../../../../src/frontends/qt4/TocModel.cpp:51
#41 lyx::frontend::TocModels::reset (this=0x895ec54, bv=0x8b4a150)
    at ../../../../src/frontends/qt4/TocModel.cpp:350
#42 0x08378fc4 in lyx::frontend::GuiView::structureChanged (this=0x8933e70)
    at ../../../../src/frontends/qt4/GuiView.cpp:1112
#43 0x080af6a5 in lyx::updateLabels (buf=..., childonly=false)
    at ../../src/buffer_funcs.cpp:561
#44 0x08188517 in lyx::Text::dispatch (this=0x8ab289c, cur=..., cmd=...)
    at ../../src/Text3.cpp:1561
#45 0x081e80ef in lyx::Cursor::dispatch (this=0x8b4a1d8, cmd0=...)
    at ../../src/Cursor.cpp:316
#46 0x08131e9c in lyx::LyXFunc::dispatch (this=0x872cf38, cmd=...)
---Type <return> to continue, or q <return> to quit---
    at ../../src/LyXFunc.cpp:1755
#47 0x08118fd0 in lyx::dispatch (action=...) at ../../src/LyX.cpp:1130
#48 0x083bea35 in lyx::frontend::Action::action (this=0x8c56438)
    at ../../../../src/frontends/qt4/Action.cpp:69
#49 0x083beac8 in lyx::frontend::Action::qt_metacall (this=0x8c56438, 
    _c=QMetaObject::InvokeMetaMethod, _id=20, _a=0xbfffe7d8)
    at ./Action_moc.cpp:77
#50 0x00ec6c9a in QMetaObject::metacall(QObject*, QMetaObject::Call, int, void**) () from /usr/lib/libQtCore.so.4
#51 0x00ed53d5 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/libQtCore.so.4
#52 0x0040bbd9 in QAction::triggered(bool) () from /usr/lib/libQtGui.so.4
#53 0x0040ddcc in QAction::activate(QAction::ActionEvent) ()
   from /usr/lib/libQtGui.so.4
#54 0x008b160c in ?? () from /usr/lib/libQtGui.so.4
#55 0x008b7abb in ?? () from /usr/lib/libQtGui.so.4
#56 0x008b8ac7 in QMenu::mouseReleaseEvent(QMouseEvent*) ()
   from /usr/lib/libQtGui.so.4
#57 0x004707f8 in QWidget::event(QEvent*) () from /usr/lib/libQtGui.so.4
#58 0x008ba0cc in QMenu::event(QEvent*) () from /usr/lib/libQtGui.so.4
#59 0x004124dc in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /usr/lib/libQtGui.so.4
#60 0x004199f7 in QApplication::notify(QObject*, QEvent*) ()
---Type <return> to continue, or q <return> to quit---
   from /usr/lib/libQtGui.so.4
#61 0x08359008 in lyx::frontend::GuiApplication::notify (this=0x86fe390, 
    receiver=0x8c55c00, event=0xbfffefd0)
    at ../../../../src/frontends/qt4/GuiApplication.cpp:1287
#62 0x00ec1a3b in QCoreApplication::notifyInternal(QObject*, QEvent*) ()
   from /usr/lib/libQtCore.so.4
#63 0x00418952 in QApplicationPrivate::sendMouseEvent(QWidget*, QMouseEvent*, QWidget*, QWidget*, QWidget**, QPointer<QWidget>&, bool) ()
   from /usr/lib/libQtGui.so.4
#64 0x004a45cf in ?? () from /usr/lib/libQtGui.so.4
#65 0x004a3511 in QApplication::x11ProcessEvent(_XEvent*) ()
   from /usr/lib/libQtGui.so.4
#66 0x004d260a in ?? () from /usr/lib/libQtGui.so.4
#67 0x0172e5e5 in g_main_context_dispatch () from /lib/libglib-2.0.so.0
#68 0x017322d8 in ?? () from /lib/libglib-2.0.so.0
#69 0x017324b8 in g_main_context_iteration () from /lib/libglib-2.0.so.0
#70 0x00eed5d5 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#71 0x004d2135 in ?? () from /usr/lib/libQtGui.so.4
#72 0x00ec0059 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#73 0x00ec04aa in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) ()
   from /usr/lib/libQtCore.so.4
---Type <return> to continue, or q <return> to quit---
#74 0x00ec469f in QCoreApplication::exec() () from /usr/lib/libQtCore.so.4
#75 0x00412577 in QApplication::exec() () from /usr/lib/libQtGui.so.4
#76 0x08121cce in lyx::LyX::exec (this=0xbffff8b8, argc=@0xbffff8e0, 
    argv=0xbffff984) at ../../src/LyX.cpp:343
#77 0x0807a081 in main (argc=2, argv=0xbffff984) at ../../src/main.cpp:46