Works fine here. When doing this ensure your timeline cursor is exactly where the cursor in your Generated Media control window is because you cannot synch Generated Media with the timeline. Thus makes often happen you change parameters while watching a different frame.
When I mean "engage" I actually DO mean "engage". Yeah, I kinda know about the non-sync thing. No, what I'm "seeing" is I can't get the CHECK tick-mark to take? It does in VP8.
You are right. This checkbox behaves strange. I can't check the Proportional box. However - if I adjust one of the parameters, either Horizontal OR Vertical and then click onto the Proportinal checkbox it equals the parameters.