Great! I was going to see if I could automate the workaround in the current Sigil launch script (test to see if XDG_CURRENT_DESKTOP is set to kde and change it to something else before launching Sigil if it is), but if a real fix is in the works, I wouldn't want to the workaround to potentially stomp all over the fix when it comes out. So I think I'll go back to my idea of adding the commented out workaround to the Sigil launch script so we can easily point people to it should they need it.
I'll also add a note to the Linux section of Sigil's WIKI about the issue, the workaround, and the potential forthcoming fix.
EDIT: Wiki updated.