Version:            (using KDE 4.1.2)
OS:                Linux
Installed from:    Ubuntu Packages

This happened with KDE3, so it's not new, but it's still there, still annoying.

I restart kmail and all is good, so it's not a particular feature of the mail I'm replying to.

Here's the backtrace:
Application: Kontact (kontact), signal SIGSEGV                                  
[Thread debugging using libthread_db enabled]                                   
[New Thread 0xb4ded6c0 (LWP 23148)]                                             
[New Thread 0xaea48b90 (LWP 23753)]                                             
[KCrash handler]                                                                
#6  0xb16da669 in KMFolder::open (this=0x22222222,                              
    owner=0xb1b6ccd2 "kmcommand")                                               
    at /build/buildd/kdepim-4.1.2/kmail/kmfolder.cpp:503                        
#7  0xb18bd1cc in KMCommand::keepFolderOpen (this=0xc6d06f8,                    
    folder=0x22222222) at /build/buildd/kdepim-4.1.2/kmail/kmcommands.cpp:457   
#8  0xb18d3880 in KMCommand::slotStart (this=0xc6d06f8)                         
    at /build/buildd/kdepim-4.1.2/kmail/kmcommands.cpp:261                      
#9  0xb18c3ef3 in KMCommand::qt_metacall (this=0xc6d06f8,                       
    _c=QMetaObject::InvokeMetaMethod, _id=4, _a=0xbfbc5ad8)                     
    at /build/buildd/kdepim-4.1.2/obj-i486-linux-gnu/kmail/kmcommands.moc:85
#10 0xb18c4482 in KMReplyToAllCommand::qt_metacall (this=0xc6d06f8,
    _c=QMetaObject::InvokeMetaMethod, _id=8, _a=0xbfbc5ad8)
    at /build/buildd/kdepim-4.1.2/obj-i486-linux-gnu/kmail/kmcommands.moc:948
#11 0xb78d0a60 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#12 0xb78d17e2 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#13 0xb78d6db7 in ?? () from /usr/lib/libQtCore.so.4
#14 0xb78d6edc in ?? () from /usr/lib/libQtCore.so.4
#15 0xb78cb53f in QObject::event () from /usr/lib/libQtCore.so.4
#16 0xb6fac8ec in QApplicationPrivate::notify_helper ()
   from /usr/lib/libQtGui.so.4
#17 0xb6fb476e in QApplication::notify () from /usr/lib/libQtGui.so.4
#18 0xb7d8a72d in KApplication::notify (this=0xbfbc6218, receiver=0xa520d28,
    event=0xbfbc5f6c)
    at /build/buildd/kde4libs-4.1.2/kdeui/kernel/kapplication.cpp:311
#19 0xb78bbe61 in QCoreApplication::notifyInternal ()
   from /usr/lib/libQtCore.so.4
#20 0xb78e9d81 in ?? () from /usr/lib/libQtCore.so.4
#21 0xb78e6520 in ?? () from /usr/lib/libQtCore.so.4
#22 0xb56d86f8 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#23 0xb56dbda3 in ?? () from /usr/lib/libglib-2.0.so.0
#24 0xb56dbf61 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#25 0xb78e6478 in QEventDispatcherGlib::processEvents ()
   from /usr/lib/libQtCore.so.4
#26 0xb7046ee5 in ?? () from /usr/lib/libQtGui.so.4
#27 0xb78ba52a in QEventLoop::processEvents () from /usr/lib/libQtCore.so.4
#28 0xb78ba6ea in QEventLoop::exec () from /usr/lib/libQtCore.so.4
#29 0xb78bcda5 in QCoreApplication::exec () from /usr/lib/libQtCore.so.4
#30 0xb6fac767 in QApplication::exec () from /usr/lib/libQtGui.so.4
#31 0x0804bf52 in main (argc=1, argv=0xbfbc6514)
    at /build/buildd/kdepim-4.1.2/kontact/src/main.cpp:218
#0  0xb80c4430 in __kernel_vsyscall ()