Suddenly random spreads has started turning grey and the page numbers says PB. I'm using CC2015. Any meaningful reason for this? Anyway to turn this "awesome" feature off?
Nope. The page area turns into a dark grey (darker than the pasteboard) and the page numbers from the master page keeps its formatting but displays PB instead of the number. Zoom level doesn't matter. And it only shows when in preview mode.
I had to keep working so I copied all the contents from these pages onto a new one and deleted the paste board/grey pages. I'll take a screenshot next time it happens.