Last time the mods could help whit my (list) post of many bugs.
I hope this is explained in shuts a way even the mods of mojang can understand it.
Ps, yes I looked thru the list of bugs and could see this one.

Duplicate items in minecraft 1.7.2 on creative

How to:

1. go in gamemode 1 (creative)
2. place a amount of items in your inventory on frame 1
3. place 1 item on frame 2
4. hold your mouse button above frame 2
5. press 1 (on your keyboard)
6. the items from frame 2 will jump to frame 1
7. and the items from frame 1 will jump to frame 2
7. the items from frame 1 are phantom (not real)
8. the items from frame 2 are real
9. if you now try to use the items from frame 1 it disappears
10. and you will see the duplicated items in frame 1 and 2

same bug no items in frame 1:

1. go in gamemode 1 (creative)
2. place no amount of items in your inventory on frame 1
3. place some items on frame 2
4. hold your mouse button above frame 2
5. press 1 (on your keyboard)
6. the items from frame 2 will jump to frame 1
7. and the items from frame 1 will jump to frame 2 << no items to move
7. the items from frame 1 are phantom (not real)
8. when used items disappear