As discussed in the linked issue, otherwise drop-down menus vanish after first use. The simple addition of "CMAKE_BUILD_TYPE=Upstream" to the wlc ebuild solved this for me. Note that this is only a workaround and no real solution exists, so it may be a good idea to do this conditional on a use-flag and let sway depend on the use-flag.
This build type only seems to influence compiler/linker flags, so enabling it would be in violation of QA, it seems to me.
See https://github.com/Cloudef/wlc/blob/master/CMakeLists.txt#L80
(In reply to Mykyta Holubakha from comment #1) > This build type only seems to influence compiler/linker flags, so enabling > it would be in violation of QA, it seems to me. This seems to be correct and I'm also totally confused how this solved my problem. Nevertheless it actually solved a rather big usability problem, so I would urge you to apply this fix until a proper solution is found. (No issue if not on my side, thanks to local overlays. ;)
Try setting the flags with /etc/portage/package.env