Cannot put item frames on top of blocks with commands

Item frames can attach to any side of a block when placed by the player. However, using /setblock or /fill it is not possible to put them on the top of a block.

Steps to reproduce

1. Cheats on.
2. Surround a single dummy block with glass blocks.
3. Stand on top of the glass block above the dummy block.
4. Use /setblock ~ ~-2 ~ frame X or /fill ~ ~-2 ~ ~ ~-2 ~ frame X to replace the block in the middle of the glass blocks with an item frame, where X is any number.
   

Expected result

Some value(s) of X result in an item frame anchored to the top of the glass block at the bottom of the glass cage.

Observed result

Different values of X result in frames anchored to the west, east, north, south, or bottom of the glass blocks, but never the top.