I have had cases where 11x14 and 16x20 RC paper settles a little after closing the easel. Looks nearly identical to negative popping. Easily 'cured' by a short pause before hitting the timer. I'll admit it took me a while to figure that one out. Watching the reflection of the safelight on the paper right after I closed the easel lead to the diagnosis.
Originally Posted by Ronald Moravec