Reproduced in 26.1-snapshot-9.
The issue seems to be with how paintings determine a direction for their offset.
In Painting#calculateBoundingBox, I replaced
Direction left = direction.getCounterClockWise();
Vec3 position = attachedToWall.relative(left, horizontalOffset).relative(Direction.UP, verticalOffset);with
Direction horizontalDirection = direction.getCounterClockWise().getAxisDirection() == Direction.AxisDirection.NEGATIVE ? direction.getCounterClockWise() : direction.getClockWise();
Vec3 position = attachedToWall.relative(horizontalDirection, horizontalOffset).relative(Direction.DOWN, verticalOffset);with a mixin, and I seems to fix the issue.
Posted again because line was too long.