Hey there Kirk,
I'm also happy to test this out for you -> I'm on osX 10.5.7
Also, one little subtle but obvious thing that you could hopefully do to clarify this is make the actual confirmation button change to say "Move" instead of "Copy" if that's what it's going to do... This may be an OS-level thing, and I'm not sure if it's feasible, but right now even if the move box is checked, I'm still ending up clicking on an item that says "copy" despite the fact that it's not actually going to do that... this inconsistency is where problems can arise...
thanks!
-jj