Editing a segment the message is different.
To reproduce:

-Create a new symbol
-Add a line using "add connected graphic lines"
-Select the line just added
-press "E" for edit, then... segmentation fault.



Thread 1 "kicad" received signal SIGSEGV, Segmentation fault.
0x00007ffff42e1518 in vtable for __cxxabiv1::__si_class_type_info () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6


Backtrace gives: 
(gdb) backtrace
#0  0x00007ffff42e1518 in vtable for __cxxabiv1::__si_class_type_info () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#1  0x00007fffda4aac87 in SELECTION::GetTopLeftItem (this=0x5555630e63a8, onlyModules=false)
    at /home/dinoghi/SANDBOXKICAD5/src/kicad/eeschema/tools/selection.cpp:69
#2  0x00007fffda45ef48 in EE_SELECTION_TOOL::RequestSelection (this=0x5555630e6310, 
    aFilterList=0x7fffda76c178 <EE_COLLECTOR::AllItems>)
    at /home/dinoghi/SANDBOXKICAD5/src/kicad/eeschema/tools/ee_selection_tool.cpp:609
#3  0x00007fffda471f9e in LIB_EDIT_TOOL::Properties (this=0x5555630f0c40, aEvent=...)
    at /home/dinoghi/SANDBOXKICAD5/src/kicad/eeschema/tools/lib_edit_tool.cpp:359
#4  0x00007fffda47729c in std::__invoke_impl<int, int (LIB_EDIT_TOOL::* const&)(TOOL_EVENT const&), LIB_EDIT_TOOL*&, TOOL_EVENT const&> (__f=
    @0x5555632a09d0: (int (LIB_EDIT_TOOL::*)(LIB_EDIT_TOOL * const, const TOOL_EVENT &)) 0x7fffda471f5e <LIB_EDIT_TOOL::Properties(TOOL_EVENT const&)>, __t=@0x5555632a09e0: 0x5555630f0c40, __args#0=...) at /usr/include/c++/6/functional:227
#5  0x00007fffda47717c in std::__invoke<int (LIB_EDIT_TOOL::* const&)(TOOL_EVENT const&), LIB_EDIT_TOOL*&, TOOL_EVENT const&> (__fn=
    @0x5555632a09d0: (int (LIB_EDIT_TOOL::*)(LIB_EDIT_TOOL * const, const TOOL_EVENT &)) 0x7fffda471f5e <LIB_EDIT_TOOL::Properties(TOOL_EVENT const&)>, __args#0=@0x5555632a09e0: 0x5555630f0c40, __args#1=...) at /usr/include/c++/6/functional:251
#6  0x00007fffda47709f in std::_Mem_fn_base<int (LIB_EDIT_TOOL::*)(TOOL_EVENT const&), true>::operator()<LIB_EDIT_TOOL*&, TOOL_EVENT const&> (this=0x5555632a09d0, __args#0=@0x5555632a09e0: 0x5555630f0c40, __args#1=...) at /usr/include/c++/6/functional:604
#7  0x00007fffda476ed7 in std::_Bind<std::_Mem_fn<int (LIB_EDIT_TOOL::*)(TOOL_EVENT const&)> (LIB_EDIT_TOOL*, std::_Placeholder<1>)>::__call<int, TOOL_EVENT const&, 0ul, 1ul>(std::tuple<TOOL_EVENT const&>&&, std::_Index_tuple<0ul, 1ul>) (this=0x5555632a09d0, 
    __args=<unknown type in /home/dinoghi/SANDBOXKICAD5/usr/bin/_eeschema.kiface, CU 0x2d31bcb, DIE 0x2d85edc>)
    at /usr/include/c++/6/functional:934
#8  0x00007fffda476b95 in std::_Bind<std::_Mem_fn<int (LIB_EDIT_TOOL::*)(TOOL_EVENT const&)> (LIB_EDIT_TOOL*, std::_Placeholder<1>)>::operator()<TOOL_EVENT const&, int>(TOOL_EVENT const&) (this=0x5555632a09d0, __args#0=...) at /usr/include/c++/6/functional:993
#9  0x00007fffda47663c in std::_Function_handler<int (TOOL_EVENT const&), std::_Bind<std::_Mem_fn<int (LIB_EDIT_TOOL::*)(TOOL_EVENT const&)> (LIB_EDIT_TOOL*, std::_Placeholder<1>)> >::_M_invoke(std::_Any_data const&, TOOL_EVENT const&) (__functor=..., __args#0=...)
    at /usr/include/c++/6/functional:1717
#10 0x00007fffda65e0e3 in std::function<int (TOOL_EVENT const&)>::operator()(TOOL_EVENT const&) const (this=0x555563ab21b8, 
    __args#0=...) at /usr/include/c++/6/functional:2127
#11 0x00007fffda65b16f in COROUTINE<int, TOOL_EVENT const&>::callerStub (aData=140737488335904)
    at /home/dinoghi/SANDBOXKICAD5/src/kicad/include/tool/coroutine.h:331
#12 0x00007fffda6be4b1 in make_fcontext () from /home/dinoghi/SANDBOXKICAD5/usr/bin/_eeschema.kiface
#13 0x0000000000000000 in ?? ()