@RoverDude
I took your request, to open another thread for this. I just took a clean 1.2 install and put in only the "USI_2016.10.16.01.zip" mod compilation and was able to reproduce the flickering by clicking the categories like crazy:
(EDIT: It seems to be NOT specific to USI, but being a stock problems that can occur, when there a to many parts in a category)
(EDIT2: Link to the flickering thread in the unmodded installs board)
(EDIT3: Could a mod please delete this redundant thread then...)
Some more background: I've trying to track this issue a long time. I thought KER is the problem. I've had this flickering since 1.1.x and also I am using plenty of USI mods.
A friend was playing vanilla and I suggested KER and soon later USI-LS... I've got the information back that after KER the flickering began. But maybe that friend mixed that up.
Yesterday in a stream someone told, that he has the flickering and is not using KER. Today I've found another guy who is using KER, has no flickering, but is also not using USI.
So this brought back my attention to USI. I've did this test in the video. Maybe this is a stock bug that USI triggers...
Hope it helps debugging.