Not for every image, but for this specific one:

And it's not the only one, since I've heard of this happening. Seems like a nasty bug if you'd ask me.
It outright refuses to set any offsets using the image/offset viewer. And just locks to the offsets the image has set - which can be changed with the non-interactive offset setter.
This also happens if the graphic is converted to Doom GFX, so it's very strange.