x11-misc/vym-1.10.0 installs into the /usr/local prefix. The only file in the correct /usr prefix is the exportvym script. I suspect the sed command in the ebuild is not correct.
Created attachment 135096 [details, diff] possible patch This fixes it on my machine. It overwrites the INSTALLDIR variable in qmake and obsoletes one of the two sed matches.
I already fixed it, but your patch is correct. Probably I'll do it your way in the next version bump. Thanks!