Item Frame drops off wall if Netherack Fence placed on wall below it.

When placing Netherack Fence on a wall beneath an an Item frame, the Item frame after about a full second pops off the wall and falls as a dropped item.

I retested and added a space between the Fram and Fence by attaching them to a Quartz wall with this alignment:

ITEMFRAME
OPENSPACE
NETHERACK FENCE

It still popped off the wall.