Quick reply...
Leafpad 0.8.17le.
Serious and reproducible (at least, for me) bug (it's possible it's a system bug triggered by leafpad; in any case, the same actions in vi don't reproduce the problem).
1. open X Terminal;
2. sudo gainroot (rootsh must be installed);
3. cd /etc/xdg/menus/
4. leafpad hildon.menu
5. edit something in the file (add a line, for instance)
6. menu->Save
7. UI is frozen; you cannot switch windows; you cannot close leafpad; Ctrl-Backspace doesn't go to thumbnails of windows; power key menu cannot be seen; you can charge the device and see the LED; you can slide the keyboard and see the lights turn on; slider works; power key allows you to shutdown.

The file is saved, as can be found after shut down - start up.

I have tried command
echo "$(leafpad hildon.menu)" > /home/user/echo
while reproducing the bug, but the echo file is empty after restart, no additional information.

What's wrong with my setup? I have updated to PR1.3 over the air, and all applications "just work", without problems.

How can I log more information about this lockup?