It is no secret that there are buffer glitching issues in Logic. From what I can tell, It hasn't been solved in L9. The reason that Logic is so efficient with CPU and plugs is because it shuts off plugin processing when no audio is present. This leads to "glitches" or little bits of what was previously in the audio buffer of certain plugins being spit out at inopportune moments. Especially at the beginning of bounces. In theory, if a plugin is coded properly to respond to the buffer flushing commands that Logic sends to the plug, it shouldn't be a problem. A lot of plugins in the past were susceptible to this "burping" because of not implementing buffer flushing commands properly. NI plugs in particular. Some people blame Apple and say Logic's implementation is buggy. There is some debate about that, but currently, of all the plugs I own, Trilogy and Omnisphere are the lone holdouts and frequently tend to cause problems. All the other ones seem to have been fixed.
FWIW: My I/O buffer is set to 512, process buffer medium, and 44.1k
1. Call up a sound, say "Arp's Golden Years" on an Omnisphere instantiated on a Logic instrument track. Any sound with a reasonably long release will work.
2. Now with Logic idling, take one hand and play a chord in the upper register.
3. While you are holding this chord down, hit the play button to start Logic's transport. The chord will stop sounding and be cut off the moment you hit play. This is normal behavior.
However, Omnishpere will also make a subtle sound somewhat like a denormaling click.
4. Let go of the chord and you can stop Logic, or keep it going--doesn't matter. Omnisphere now has this chord in it's audio buffer, and it has not been properly flushed. Normally the buffer should be emptied at this point.
5. Now hit a very low note on the keyboard, and listen as you hear the remnant of the upper chord (what would have been its natural release segment) the moment you hit the low note. Logic can be in play or idle, it doesnt matter because Omnishpere now has crap in it's buffer which will get spit out no matter what you are doing, as soon as the next MIDI note triggers it.
That is the behavior that Omnisphere shouldn't be doing. The buffer should have been emptied.
You can repeat steps 1-3 with other plugs and most will not exhibit the behavior in steps 4-5. I just tried it with Absynth and it did not do this, and I tried it with an ES2 and it did not do this.
Let me know if anyone can repeat. I couldn't get anywhere with tech support on this.