It would be pretty sweet if we could manually rotate tiled backdrops, via a "lever" similiar to sprites.
I'm not sure how troublesome it would be to implement, but it can't hurt to suggest
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Since tiled backgrounds support behaviors, I suspect it may be possible with modification.
Until then, rotate your shape and copy it 4 times for each corner in the picture editor
Just needs a flag adding to the SDK to enable the lever.
Whether the drawing code supports rotating (as it tiles it with special coordinates I think) is another matter.