Can't Preview Other Users Posts as Admin!

A few months ago we started noticing that if we attempt to edit a contributors posts or anyone else's posts but our own, we are unable to use the Preview function. WP pops up a vague message saying we don't have the access to do it. If we SAVE the edit (which then means it's live of course) we can Preview all we want.

Has ANYONE seen this issue or have ANY idea how to go about tracking it down or fixing it?

Poster :