When maps are placed in an item frame, you can use the 'pick block' function to get a copy of the map in creative, but if you are not looking at the center of the map (where the item frame usually is without a map in it) then it will get the block below it

What I expected to happen was...:
I should've gotten a copy of the map

What actually happened was...:
I got the block the item frame was on

Steps to Reproduce:

1. place item frame down (in my case it was on the ground but I don't think that matters)
2. place a filled out map into the item frame
3. use 'pick block' (for me this is 'R' but it defaults to middle click) to get a copy of the map
4. If you are looking at the center of the block, you will get a copy like you should, but if you are looking at the corner of a block, you will get the block the item frame is on