It is indeed the case. The sharing mechanism depends on cascading assignment of license of publication rights, and the thumbnailing/cropping for timeline/feed e

It is indeed the case. The sharing mechanism depends on cascading assignment of license of publication rights, and the thumbnailing/cropping for timeline/feed entries requires rights to create derivative works (which, unfortunately, has the side-effect of permitting almost any sort of derivative work that wouldn't be covered by libel). Although you still retain copyright (and can separately license works outside of Facebook under other terms), you are granting extremely broad and transferable rights (the "friends" chain can get to be pretty long once sharing is allowed) to a work by posting it to Facebook. If you don't want to relinquish control of a work, don't post it on FB. Never post images of value in a valuable size, and watermark the hell out of anything that is low-res and commercial.