Audio Export Strange BEhaviour

I have posted this a few days ago on the issues page to no avail. Anyone here experienced these problems?

I’ve been exporting stems on 7.5.10 yesterday and today only to find that things are sometimes exporting and sometimes not. The signal path is good. I hear audio before exporting. I see the meters moving if I try it in real time export. It all works perfectly if I open the project in previous versions of Cubase.
Also, when exporting the same length items (more than 1 stem) the file data sizes are showing different sizes and often double what’s expected. Never had that happen before either.
I have tried different bit rates and sample rates, stereo and mono. With and without plugins. I’ve created fresh tracks. Still the problems occur.
Another thing which may or may not be significant is that sometime the file exports with some or all of the audio not showing in previews of the file in various editors. The sound is there sometimes but does not show in the preview field. This includes Cubase’ project window if I export to the pool. However if I ask Cubase to add an export to the pool it gives me a good clean file there - of the expected length and size. I will use this as a work around for now but this is very worrying behaviour.
I am delivering stems to a dubbing house today and this is a huge issue. It also makes me wonder if anything else has been missing in exports over the last month or 2…?!
Has anybody else had these problems? Can’t find anything on the forums.

Mac Pro, 10.8.5, 32GB Ram. 1 Waves plugin inserted and 1 NI Reverb but have tried with and without these to rule them out. Tested using various 3rd party editors including Soundforge, Peak, DSP Quattro etc.

And to update - I went back to ver.7 and got the project exported with no problems whatsoever.