When item frames are placed on the bottom of blocks and are destroyed, the item frame and any item it contains shoots out of the top of the nearest air touching block in a vertical 3x3 column (tested in creative mode). There doesn't appear to be a height limit to the column of blocks that the item frame can travel up.

This makes it impractical for players with underground bases as their item frames and items inside in survival mode may effectively disappear. In fact I discovered this bug in survival mode when I tried to place a map on the ceiling of an underground base, and lost the map when I destroyed the item frame. Luckily I made a copy, but some special items to players may get lost this way.