I've not had problems but others have. I suspect it depends on how variable the frame rate is. When shooting in good light it doesn't vary much but in poor light conditions the rate can get low and this I suspect is where problems arise.
Thank you all, I agree that converting is a fine workaround, and surly it's better to use programmers time on more useful tools if batch converting can be done in many external tools. I hardly use VFR clips, and the few I had gave me no trouble in my "other" NLE.
* I use XMedia Recode portable and dumped all the other converters.