Hi Stas,
Sorry, I never noticed the notification for this email. It sat in the pending queue for 9 days. Probably you've long since moved on, but to answer your question in case it helps, ScalaTest does create a class loader for each run, parallel or not, except when running with sbt, sbt passes ScalaTest a class loader to use via the framework API, so we just use that one. I don't know what "concurrentRestrictions in Global" does, so I think you may have more luck on the sbt side asking over in the sbt mailing list or discussion groups.
Bill