I have a similar issue in whatever version of logic 8 I am using. Sometimes it happens, sometimes it doesn't. Sometimes during an offline bounce a bit of what happens later in the song prefaces the start of the song! That doesn't happen very often, and usually when I bounce it a second time it doesn't happen again. But it sure is a little weird.
Yes, i know it's a bug with Logic, but other developers have updated their plugins to fix it too. I'm hoping that Nebula can be updated because we all know that Apple is not going to fix the bug just for Nebula because currently, Nebula is the only plugin that is doing it anymore.
I'm also experiencing a random bug in which nebula causes all audio to drop out from logic until I restart it. This happens randomly when I skip to a different position of the sequencer with the playhead.
its mega annoying. What i have to do is put some silence at the start or end of a project on every track so it cleans out the buffer before it actually starts playing the real audio. Seems to work. But yes this needs to be resolved. This has been an issue since last year-see an old thread of mine