At the very least it's a change in behavior. It looks like the counter limit now uses a ceiling check instead of a floor. A request has been made internally for some clarification. Generally, of course, loops using non-integral values are to be avoided due to potential precision issues, but you're showing a different case completely that's unrelated.

The behavior of IDL in the case of FOR loops using floating point indexing will be addressed in a future release, returning it to its original state.

Thanks for checking Jim. And no, I wouldn't normally use this, but I was going through someone else's code when coming across this illogical behaviour.