When a Bell is powered, it swings in the direction that is corresponding to it's "facing" state - this is fine when the bell is on the floor, even on ceiling.
The problem arises when the bell is hanging from a wall, as then the bell will swing:
 a) away from the wall it is attached to into air (when "facing: single_wall")
 b) away from the wall it is attached to into it's own stick (when "facing: double_wall")
While it could somehow be reasoned that this is fine for the single wall, it definitely is not the case for the double wall. Further more, to back this argument, when a bell is hung from the side of a block, players can play the bell only from the sides, not being able to play it from, or into, the wall.
My proposition would be to either
 add a case for N/S wall bells to play only in E/W directions when powered and a case for E/W to play only in N/S directions when powered (idk, make it randomly choose  one of the 2 possible directions I guess?)
 or (in degrees), always add 90° to the direction of bell play animation when powered, when it is attached to a wall.

Also yes - this is just a minor graphical bug but while I can agree it is a very low priority, similar bugs have been fixed in the past so I think this one should get a fix someday too.