### start fluxbox (w/o any config) under Xephyr w/ xinerama
### $ Xephyr -br -ac -noreset -no-host-grab -glamor +xinerama +extension RANDR -screen 1280x720 -origin 1280,0 -screen 640x480 -origin 0,240 :50
### click Configuration->Toolbar->On Head->All Heads

Program received signal SIGSEGV, Segmentation fault.
0x0000555555680d3b in FbTk::RefCount<FbTk::Command<void> >::incRefCount (this=0x7fffffffd7a0) at src/FbTk/RefCount.hh:132
132         (*m_refcount)++;
(gdb) bt
#0  0x0000555555680d3b in FbTk::RefCount<FbTk::Command<void> >::incRefCount (this=0x7fffffffd7a0) at src/FbTk/RefCount.hh:132
#1  FbTk::RefCount<FbTk::Command<void> >::RefCount (copy=..., this=0x7fffffffd7a0) at src/FbTk/RefCount.hh:84
#2  FbTk::MenuItem::click (this=0x555555750a10, button=<optimized out>, time=<optimized out>, mods=<optimized out>) at src/FbTk/MenuItem.cc:44
#3  0x000055555567f082 in FbTk::Menu::buttonReleaseEvent (this=0x5555559bd000, re=...) at src/FbTk/Menu.cc:944
#4  0x00005555555a9613 in FbMenu::buttonReleaseEvent (this=this@entry=0x5555559bd000, be=...) at src/FbMenu.cc:68
#5  0x000055555558d21a in ToggleMenu::buttonReleaseEvent (this=0x5555559bd000, ev=...) at src/ToggleMenu.hh:42
#6  0x0000555555668888 in FbTk::EventManager::dispatch (this=0x5555556ef420 <FbTk::EventManager::instance()::ev>, win=2097579, ev=...,
    parent=parent@entry=false) at src/FbTk/EventManager.cc:191
#7  0x00005555556689f2 in FbTk::EventManager::handleEvent (this=<optimized out>, ev=...) at src/FbTk/EventManager.cc:48
#8  0x00005555556191b3 in Fluxbox::handleEvent (this=0x55555572b420, e=0x7fffffffda80) at src/fluxbox.cc:619
#9  0x0000555555619b44 in Fluxbox::eventLoop (this=0x55555572b420) at src/fluxbox.cc:542
#10 0x000055555558b465 in main (argc=1, argv=0x7fffffffdff8) at src/main.cc:210
(gdb)