I have been playing on a world which was created before version 1.7.2. I have had some old flower pots, so when I decided to relocate them, and broke them, they only dropped themselves and no plants which were inside them!

Only flower pots which were put to the world before version 1.7.2 are affected, any new flower pots drop both the plant and themselves.

EDIT: The world was created in Minecraft 1.4 (Pretty Scary Update).
Sometimes, instead of not dropping anything at all, old (and new too) flower pots still drop two flower entities instead of one.

EDIT 2: attached two crash reports