I tested this scenario in Reaper x64 - no problem there. (But I am a Sonar user for now...)
When I insert an instance of Nebula (the typically recommended "reverb" version with the high DSP buffer setting) on a track other than the one I have automation on, it throws off the synchronization between the automation and the audio by a consistent amount. The audio does not lose sync with other tracks.
This is related to delay compensation I believe. If delay compensation is turned off in Nebula's properties in the Plug-In Manager of Sonar, automation and audio will be in sync again (in the situations I tested), but audio is out of sync with other tracks.
If I have only one instance of Nebula on in the whole project and it is on the track with automation, automation is in sync. Moving this instance to another track and/or having other instances on other tracks throws it off again.
When I bounce (offline - not real time) the track or clips, there is no problem, regardless of other instances of Nebula.
When Nebula's DSP buffer is decreased, synchronization is less off, but additional instances will make it more out of sync again.