It seems our output silence/vst scrambling  issue is related to the most recent Omnisphere update. This release was early June. I've since loaded an old dll of Omnisphere from January (not ideal) and this works.  Whether the latest update to Cakewalk has made the Omnisphere dll unstable is unknown. Its only when I went back to a project pre-June Omnisphere release did I realise that there was an issue. I cant confirm though if this affects projects that use Trilian or Stylus RMX yet.