I have never read that it works just like tab, thankfully. There is a macro posted on the wiki that uses /targetenemy and what it does is it cycles through the targets so you can dot them. The macro is also setup to keep you from selecting the same target twice.

edit: I just read a few places that made that 'acts like tab' statement, but I haven't noticed it to work that way. I does act like tab in that it targets the closest enemy but I was under the impression that it won't advance until you do something to that target. I may be wrong, that is just how I have used it.