Placing two item Frames in one block (rightclick on edge of block) will make them placed in another.
If you place a map into one of These, the other Frame is glitching though the one, with the map inside.
MC-32000
2 Item Frames on one Block and Map in it
Resolved
Duplicate
0
Kajanor
(Unassigned)
Unconfirmed
Minecraft 13w38c
Retrieved
I don't see the bug here. If two item frames are occupying the same space, weird stuff will happen.