^ Interesting. I tested this out. Juni is a very complex girl indeed.
I made tiles with pixel heights 1 to 12. I put these in the target location to see exactly where Juni shifts to. Then, I tried shifting to a location on the same screen and an identical relative location on another screen. I used different shift shapes. I used absolute shifts and relative shifts. I shifted from locations above, below, and even with the relative target location. I tried shifting while standing still, while running, and while falling. I tried with and without quantizing.
I got so many different results I couldn't keep track of it all. While running into a square shift with absolute targeting, up to 6 pixels on the target location won't cause a swim. Try the same thing with relative targeting and 1 pixel causes a swim. Use absolute targeting again while standing still and 5 pixels causes a swim only part of the time. Disable quantize in this last scenario and she'll still appear up to 5 pixels above 0. (She started at 0.)
At any rate, none of this made the 'sticky' work better. I've already walled her in my level.
Edit: By the way, I agree that it's not a bug. If I used the engine the way it was meant to be used, these fine details wouldn't be an issue.