Scenario(s)/Conditions:

1. Have 2 maps: 1 cloned from the other.
2. Place 1 copy in an item frame and the other in your offhand.
3. Save and Exit.
4. Load world
5. Remove copy from frame and allow Steve (player character) to pick it up.
6. See that the copy stacks into the offhand.
7. Attempt to remove a single copy or both copies from Steve's offhand.

What I expect to happen...

the portion the player selects can be placed in the inventory or hotbar as with any other item that is or can be stacked.

What actually happens...

the portion the player selects immediately jumps back into the offhand.

One Known Workaround:

1. Save and Exit with both maps in Steve's offhand.
2. Reload world
3. Player can now manipulate stack of maps in offhand as expected.