The UAD v6.5.2 is a patch fix for (2) "show stopping" nasty bugs in PT & Cubase. In PT, UAD presets were not getting properly saved/recalled in PT projects (probably RTAS related). Cubase would crash when using UAD plug-ins in RAM intensive projects. What "show stopping" bug were you expecting to get fixed in SONAR? Personally, UAD v6.51 has been working fine for me using the x64 plug-ins exclusively in SONAR X2a x64.
The one issue I have is UA no longer including the "mono (m)" versions of new UAD VST plug-ins since version v6.4. I have not heard much of a peep from SONAR/UAD users about it. Either SONAR/UAD users are totally clueless about the importance of using the mono (m) versions (less DSP load) or don't mind using extra DSP up needlessly on their mono tracks/sources. Try adding one of the new LA2A plug-ins to a SONAR project on a mono track/source. Look at your DSP meter and you will see a 21.1% load. Mono (m) versions would use only 16.2% per instance. That is about a 25% savings. Of course, all of the UAD plug-ins pre v6.4 still have the mono (m) versions, it is just any new plug-ins from v6.4 on.
I fired off a strongly worded letter to UA customer service a few months back about my displeasure with this ill advised move. I encourage other SONAR/UAD users to do so as well. In talking to UA support there seems to be some internal discussions about bringing the mono(m) versions back for new UAD VST plug-ins, but the more they hear from the users of the DAW apps affected (SONAR, REAPER, Live, Samplitude, SSL/Soundscape, ACID Pro, Vegas, Harrison Mixbus, etc..) the better off we are to get the outcome we want.
Cheers,
Billy Buck