Well something happened with R4 that breaks my whole UI. Not so happy about that. Bigger issues is I can't figure out what the fix is.
The window below looks fine in R3, no black background on the canvas. In r4 some of my canvas images display a back background where as others are correctly transparent.
The icons in the middle section of the window all have the same settings but one has the black background artifact, the others do not.
The top portion of the window has canvas over a rectangle, the middle section has canvases over a page panel.
All the options in the inspector window under behavior heading are disabled.
Would like to file a bug report but right now i'm not sure how to reproduce. Specifically why it affects some canvases but not others. Just rolled back to R3 and everything works again, so that rules out the images being corrupted.