I just ran into this one. Hamish Rodda also reproduced it.

Using host libthread_db library "/lib/libthread_db.so.1".
`system-supplied DSO at 0xffffe000' has disappeared; keeping its symbols.
[Thread debugging using libthread_db enabled]
[New Thread 16384 (LWP 19690)]
[KCrash handler]
#6  0xb71bcf1a in QLineEditPrivate::setText ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#7  0xb71c00f7 in QLineEdit::setText () from /opt/qt-copy/lib/libqt-mt.so.3
#8  0xb5fa1034 in KateExternalToolServiceEditor::KateExternalToolServiceEditor
    () from /opt/kde_trunk/lib/libkateinterfaces.so.0
#9  0xb5fa1f7c in KateExternalToolsConfigWidget::slotEdit ()
   from /opt/kde_trunk/lib/libkateinterfaces.so.0
#10 0xb5fa4b84 in KateExternalToolsConfigWidget::qt_invoke ()
   from /opt/kde_trunk/lib/libkateinterfaces.so.0
#11 0xb70ea184 in QObject::activate_signal ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#12 0xb70ea91c in QObject::activate_signal ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#13 0xb744ac7c in QButton::clicked () from /opt/qt-copy/lib/libqt-mt.so.3
#14 0xb71821a1 in QButton::mouseReleaseEvent ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#15 0xb7124084 in QWidget::event () from /opt/qt-copy/lib/libqt-mt.so.3
#16 0xb708635f in QApplication::internalNotify ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#17 0xb70865b6 in QApplication::notify () from /opt/qt-copy/lib/libqt-mt.so.3
#18 0xb7700385 in KApplication::notify ()
   from /opt/kde_trunk/lib/libkdecore.so.4
#19 0xb701eb8a in QETWidget::translateMouseEvent ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#20 0xb701cdfc in QApplication::x11ProcessEvent ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#21 0xb7030b35 in QEventLoop::processEvents ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#22 0xb709cb01 in QEventLoop::enterLoop () from /opt/qt-copy/lib/libqt-mt.so.3
#23 0xb70854ef in QApplication::enter_loop ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#24 0xb7280442 in QDialog::exec () from /opt/qt-copy/lib/libqt-mt.so.3
#25 0xb5f87bfc in KateMainWindow::slotConfigure ()
   from /opt/kde_trunk/lib/libkateinterfaces.so.0
#26 0xb5f8d13c in KateMainWindow::qt_invoke ()
   from /opt/kde_trunk/lib/libkateinterfaces.so.0
#27 0xb70ea184 in QObject::activate_signal ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#28 0xb70ea91c in QObject::activate_signal ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#29 0xb7a24199 in KAction::activated () from /opt/kde_trunk/lib/libkdeui.so.4
#30 0xb7a24d6a in KAction::slotActivated ()
   from /opt/kde_trunk/lib/libkdeui.so.4
#31 0xb7a2a929 in KAction::slotPopupActivated ()
   from /opt/kde_trunk/lib/libkdeui.so.4
#32 0xb7a2ac25 in KAction::qt_invoke () from /opt/kde_trunk/lib/libkdeui.so.4
#33 0xb70ea184 in QObject::activate_signal ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#34 0xb74438ed in QSignal::signal () from /opt/qt-copy/lib/libqt-mt.so.3
#35 0xb7104d71 in QSignal::activate () from /opt/qt-copy/lib/libqt-mt.so.3
#36 0xb71fa737 in QPopupMenu::mouseReleaseEvent ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#37 0xb7a12b41 in KPopupMenu::mouseReleaseEvent ()
   from /opt/kde_trunk/lib/libkdeui.so.4
#38 0xb7124084 in QWidget::event () from /opt/qt-copy/lib/libqt-mt.so.3
#39 0xb708635f in QApplication::internalNotify ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#40 0xb70865b6 in QApplication::notify () from /opt/qt-copy/lib/libqt-mt.so.3
#41 0xb7700385 in KApplication::notify ()
   from /opt/kde_trunk/lib/libkdecore.so.4
#42 0xb701ede0 in QETWidget::translateMouseEvent ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#43 0xb701cdfc in QApplication::x11ProcessEvent ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#44 0xb7030b35 in QEventLoop::processEvents ()
   from /opt/qt-copy/lib/libqt-mt.so.3
#45 0xb709cb01 in QEventLoop::enterLoop () from /opt/qt-copy/lib/libqt-mt.so.3
#46 0xb709ca56 in QEventLoop::exec () from /opt/qt-copy/lib/libqt-mt.so.3
#47 0xb70854bf in QApplication::exec () from /opt/qt-copy/lib/libqt-mt.so.3
#48 0xb5fe5059 in kdemain () from /opt/kde_trunk/lib/libkdeinit_kate.so
#49 0xb5fe8884 in kdeinitmain () from /opt/kde_trunk/lib/kde3/kate.so
#50 0x0804e5a3 in launch ()
#51 0x0804edbb in handle_launcher_request ()
#52 0x0804f386 in handle_requests ()
#53 0x0804fb91 in main ()

Created an attachment (id=16169) [details]
Patch for #121607

This fixes #121607 for me by simply checking if a separator is selected to 
prevent the crash. The Edit Button won't get selected in that case.

The patch look sane to me indeed.
Will apply later - thanks a lot.

SVN commit 542434 by dhaumann:

fix crash in external tools config when clicking the edit button.
CCBUG:121607


 M  +1 -1      kateexternaltools.cpp  


--- branches/KDE/3.5/kdebase/kate/app/kateexternaltools.cpp #542433:542434
@@ -719,7 +719,7 @@
 {
   // update button state
   bool hs =  lbTools->selectedItem() != 0;
-  btnEdit->setEnabled( hs && static_cast<ToolItem*>(lbTools->selectedItem()) );
+  btnEdit->setEnabled( hs && dynamic_cast<ToolItem*>(lbTools->selectedItem()) );
   btnRemove->setEnabled( hs );
   btnMoveUp->setEnabled( ( lbTools->currentItem() > 0 ) && hs );
   btnMoveDwn->setEnabled( ( lbTools->currentItem() < (int)lbTools->count()-1 )&&hs );

SVN commit 542438 by dhaumann:

fix crash in external tools when clicking the edit button on separator items
(If further crashes happen, please report.)
BUG:121607


 M  +1 -1      kateexternaltools.cpp  


--- trunk/KDE/kdebase/kate/app/kateexternaltools.cpp #542437:542438
@@ -757,7 +757,7 @@
 {
   // update button state
   bool hs =  lbTools->selectedItem() != 0;
-  btnEdit->setEnabled( hs && static_cast<ToolItem*>(lbTools->selectedItem()) );
+  btnEdit->setEnabled( hs && dynamic_cast<ToolItem*>(lbTools->selectedItem()) );
   btnRemove->setEnabled( hs );
   btnMoveUp->setEnabled( ( lbTools->currentItem() > 0 ) && hs );
   btnMoveDwn->setEnabled( ( lbTools->currentItem() < (int)lbTools->count()-1 )&&hs );