I recently upgraded to SX 7.1.28 (Meaning I am up to 7.1.23 plus the latest fix files) and I am having the occasional problem with right clicking on a channel. Sometimes all I get is an empty narrow box.
Also I have had the same happen in dropdown menus for the Child or 3D menu, I drops down, but the menu is empty. It does not happen all the time and each time that it has done it I just logged off and reopened the software. And it starts working right again.
Currently my software is working correctly but the next time it acts up I will get some screen grabs of the behaviour.