kkgd, not sure what your definition of "trading" is but there have been large blocks (both odd and even numbers... like 160,000 or 254,432 for example only as I don't remember the actual numbers but that is close) going through up to ~20 minutes after market close this last week.
Also, I have had orders that I may put in with 2 minutes left in trading hours that go through up to several minutes after market close (normally ~30 seconds though) which do NOT affect the closing price. Those are after hours trades.
So, while I agree there is not supposed to be after hours trading in the pinks, after hours trades do occur. The cases where my orders execute 30 seconds or a couple minutes after market close is not really what I'd consider after hours trading (even though it doesn't affect the closing price) but the large block examples we were talking about after hours are happening. Whether you want to call that "trading" or not there is something different going on than what is normally seen.