Well I had a vague recollection that actually I'd seen this before. It was raised
here in 2007 and fixed in R2.56. I guess it was broken again later. The latest version I've just tried is R3.043.62 and it's still busted in there.
It's actually nothing to do with short lines, it's simply when you have any arc following any line where "stop cv on angles >" is ticked.
So Dave, if you absolutely must turn CV off selectively, here's "A" solution for you. Just stick a G61 and a G64 in your code at the appropriate places. There are other ways but this seems as easy as any.