Plugin audio buffers are emitted when unbypassed. This is undesirable because it spews unrelated audio contents at arbitrary places into the mix.
Heres a video of it in action…
As you can see, by the track meter, when altiverb 6 is unbypassed its audio buffer is purged onto the track. This audio is unrelated to any audio at the time the unbypass occurs and is “garbage” (unwanted) audio ejected into the mix. This is reproducible with UAD plugins as well (tested EMT 250, 1176). I could not repro this with Steinberg’s VST 3 mono delay, reverence, roomworks se, or VST 2 da tube plugins.
-Why does this occur?
I previously reported this issue here http://www.steinberg.net/forum/viewtopic.php?f=76&t=4521