No idea what version of CA you're using, but there was a bug a couple months ago that did that intermittently.
That, and if you have multiple browser tabs open to CA concurrently, but the appfeed gets updated by Window B (as it was opened last), but you install from Window A, there's a chance depending upon what happened with the feed that the references are out of sync. Edge case that's a real PITA to fix and basically requires a top-down rewrite of the whole thing.