I'm the current maintainer of Wesnoth in SBo and yes, i used KDE on my daily basis, so i found it working fine on my system and since i don't have E17 and fluxbox on my system, i can't reproduce it on my system. I also used 32 bit machine, but i don't think it would cause some problem when clicking. I think it's DE's related.
so far, i didn't find any bug report about this before, but i will try to help solve this problem out.
First, i need some information from you:
1. Have you used the latest SlackBuild or do you perform an upgrade using an old SlackBuild and changed the VERSION line instead?
2. I'm assuming you are using 1.10.5. Am i correct?
3. Have you tried to remove .wesnoth and restart the application? There's a possibility of having this problem due to an old configuration
4. Do you use full screen of windowed mode?
I found a patch for sdl that might be the culprit
If you don't mind, head to my SlackHacks
and try to rebuild SDL and then followed by wesnoth rebuild.
Hopefully this should fix your clicking bug.
Anyway, let me know if it's working since i might have to report this to Patrick if it happened to fix the problem as it might affect other application as well.
I have built E17 and installed Fluxbox on my machine and tested the new SDL package and rebuilt Wesnoth afterwards and i'm able to click on every buttons. So i can confirm that the SDL package is the culprit. You may want to recompile SDL with the patch available on my SlackHacks repository above