The texture application for the rear face (side faces untested) of the painting appears to be flipped from what it should be. The painting back texture itself seems correctly oriented, so the painting model is at fault.

left; painting, right: real blocks

Suggested Fix

It may be possible to fix this by converting paintings over to use block models like item frames currently do, and the UV settings would become configurable that way. This issue would likely end up fixed in the process.