Generally I can extend it and shorten it but not move it.

But then sometimes I can move it but it requires a technique that I cannot replicate at will. The transparency effect needs to be made solid (white) and then it can be moved but only if the stylus is away from the 'grab' marks at the extreme right. However the solid white normally only appears when those grab marks are tapped. The trick is to get it solid by tapping away from the grab marks. Sometimes I can get it, mostly not.

So I would hazard a guess that it is a bug.