In older builds of SU thumbnails would show the model exactly as it looked when saved, showing the full display area, now it zooms right in. This should be changed back or at least be an option!
FYI: This can be affected by Window > ModelInfo > File > Redefine thumbnail on save
Also as of v15.3.x, the thumbsup.dll has a regression bug in it, and certain Windows users have to rename it to prevent file locking issues.