Backtrace from GDB, just in case that helps.
(gdb) backtrace
#0  0x00007ffff5f05445 in __GI_raise (sig=<optimized out>)
    at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#1  0x00007ffff5f08bab in __GI_abort () at abort.c:91
#2  0x00007ffff5efe10e in __assert_fail_base (fmt=<optimized out>, 
    assertion=0x7ffff5a7b293 "right", 
    file=0x7ffff5a7b220 "/build/buildd/projectm-2.0.1+dfsg/src/libprojectM/MilkdropPresetFactory/Expr.cpp", line=<optimized out>, function=<optimized out>)
    at assert.c:94
#3  0x00007ffff5efe1b2 in __GI___assert_fail (
    assertion=0x7ffff5a7b293 "right", 
    file=0x7ffff5a7b220 "/build/buildd/projectm-2.0.1+dfsg/src/libprojectM/MilkdropPresetFactory/Expr.cpp", line=161, 
    function=0x7ffff5a7b3a0 "float TreeExpr::eval_tree_expr(int, int)")
    at assert.c:103
#4  0x00007ffff5a5c962 in TreeExpr::eval_tree_expr(int, int) ()
   from /usr/lib/libprojectM.so.2
#5  0x00007ffff5a5c804 in TreeExpr::eval_tree_expr(int, int) ()
   from /usr/lib/libprojectM.so.2
#6  0x00007ffff5a475f2 in PerPixelEqn::evaluate(int, int) ()
   from /usr/lib/libprojectM.so.2
#7  0x00007ffff5a3f18e in MilkdropPreset::evalPerPixelEqns() ()
   from /usr/lib/libprojectM.so.2
#8  0x00007ffff5a3f6e8 in MilkdropPreset::evaluateFrame() ()
---Type <return> to continue, or q <return> to quit---
   from /usr/lib/libprojectM.so.2
#9  0x00007ffff5a3f930 in MilkdropPreset::Render(BeatDetect const&, PipelineContext const&) () from /usr/lib/libprojectM.so.2
#10 0x00007ffff5a096e0 in projectM::renderFrame() ()
   from /usr/lib/libprojectM.so.2
#11 0x00007ffff55163f0 in QGLWidget::glDraw() ()
   from /usr/lib/x86_64-linux-gnu/libQtOpenGL.so.4
#12 0x00007ffff6931281 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#13 0x00007ffff6936179 in QObject::event(QEvent*) ()
   from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#14 0x00007ffff6e3f894 in QApplicationPrivate::notify_helper(QObject*, QEvent*)
    () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#15 0x00007ffff6e44713 in QApplication::notify(QObject*, QEvent*) ()
   from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#16 0x00007ffff691ce9c in QCoreApplication::notifyInternal(QObject*, QEvent*)
    () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#17 0x00007ffff694e1f2 in ?? () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#18 0x00007ffff694bc0d in ?? () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#19 0x00007ffff4448d53 in g_main_context_dispatch ()
   from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#20 0x00007ffff44490a0 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#21 0x00007ffff4449164 in g_main_context_iteration ()
---Type <return> to continue, or q <return> to quit---
   from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#22 0x00007ffff694c3bf in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#23 0x00007ffff6ee7d5e in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#24 0x00007ffff691bc82 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#25 0x00007ffff691bed7 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#26 0x00007ffff6920f67 in QCoreApplication::exec() ()
   from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#27 0x000000000040acff in main ()