This morning, i read LQ and there was a new report of Wesnoth not working in Slackware64-Current by Stephen Morgan. He said that he was using E17 and Fluxbox when he found out the click event is not properly handled, thus wesnoth can't be played. Since i am the maintainer of Wesnoth in SBo, i tried to find the solution on this problem.
What makes me curious is that it didn't happened on KDE and Stephen himself confirmed that in KDE, it works normally. So, i googled a little bit and found a patch from ArchLinux that were uploaded since 2010, but apparently it was never included in Slackware's SDL package since there were no bug report against it. I also ran KDE on daily basis, so i never experienced this problem before.
I tested this by rebuilding SDL package on Slackware and add this single patch and rebuilt Wesnoth again and run it on E17 (i had to built this as well to test using the same environment that Stephen used) and Fluxbox. The result was a success as i can click properly when playing Wesnoth. So, it seems that the patch did work.
I have uploaded the patch and updated SlackBuild in my SlackHacks repository just in case you want to try it on your machine. You will have to download the rest of the source package of SDL if you want to try recompiling it on your machine.