The SyncWithTableOfContents button too often doesn't work.
It has two failure modes (at least)
#1: The page isn't in the TOC, so Sync cannot work.
e.g.: This page p_active_form
#2: The page is in the TOC, and SyncToTOC sometimes works, but often/usually it doesn't - presumably because somehow the state of the help tool is weird.
I don't have an example handy, but I've often had this problem -- where sync to toc fails until I restart SlickHelp and try again.
I've also been using QtAssistant for the CMake help files.
CMake help files seem to have the opposite problem with the index that slick does -- it has far too many things it its index, where Slick has too few. (In CMake help, use the index to find "add_executable": A "ChooseTopic" dialog appears with a few dozen possible matches)
I haven't seen problem #2 with CMake help though.