It must be sticking to the side of the keg enough to hang up until you move it. If you can, add a little weight and it should work better. The Ballandkeg floating tubes have a fairly heavy piece of SS tubing in the end so I think that's why mine don't do the same thing.
I think I'll try adding weight. I have another keg buoy I haven't installed and it seems that the tubing is stiff enough that it could prop the inlet tube up, and that tube is very thin and light.