This may be Logic 9 specific...
For those of us spoiled by using MIR's 0 latency settings in the VEP 5 world, it may not be possible with the plugin.
I was running 0 latency in MIR as always, when a couple of instruments began displaying erratic volume increases.
The snare drum for example played nice and low as long as it's track was selected but as soon as I select a different track,
the snare drums volume increased dramatically.
I wasted a great deal of time chasing this, trying to determine if I had a false Midi sender somewhere.
When all else failed I bypassed the MIR Plugin and the snare drum behaved properly.
Finally I changed the MIR latency setting to match Logic or double it, and the problem went away completely.
It is nice to see Logics cores working with VSL (without a major workaround)....
P/S: I am very aware of known erratic volume issues in Logic 9, I myself had never experianced them before.