The confirmation dialog works unexpectedly on the sequence below.
1) Run uim-pref-gtk
2) Modify a value
3) Press close button of the application window (not cancel button)
4) Press "No" of the confirmation dialog
5) uim-pref quits even if answered "No"
I cannot reproduce the bug.
If you still have the problem, please investigate your environment and reopen
I've found that the bug is reproduced on Fedora Core 5.
Fixed in r3388.