Item frames can be stacked on a wall. To replicate this issue, it is best to start in Creative mode.
1. Place an item frame on the wall.
2. Attempt to place another item frame on the remaining visible edge of the block the item frame is on. The hand moves as if placing an item frame.
3. Change gamemode to Survival.
4. Attempt to break the item frame. It will fall to the floor as a resouce, but also remain on the wall.

One more punch will show the frame working as normal.

Odd thing is, this works for any amount of "stacked" item frames - put 20 on the wall, and you can punch 20 off.

It will work in any gamemode - if you place them in Survival, it consumes an item frame each time you place one. If you break them in Creative, they disappear one by one, no resource dropped.

The bug was detected in Craftbukkit Beta 1.4.4, but was replicated immediately afterwards on a 1.4.4 Vanilla Server, no mods. I am using the 1.4.5 pre-release client, and another player has replicated it with 1.4.4 client.

Two players on the server have replicated it so far.

Furthermore, I can replicate the issue in a vanilla client, on a singleplayer world, client 1.4.5-PR.

The screenshot attached shows the crosshair on the outer edge of the block, which is where you should place additional item frames.

Regards,

Xavier