You can check this with the example 3 from this archive:
The sounds are played erratically: 3 sounds at a similar interval, then the fourth at a different interval. And yet the orders are sent regularly: I checked this by printing the time to the console.
I noticed this with pygame 1.9.2-pre and Python 2.7 (Windows XP). The problem doesn't appear with pygame 1.7.1 and Python 2.5 (Windows XP) and pygame 1.7.1 and Python 2.4 (Linux Xandros for eeePC).
similar problem: I noticed (in this example or a similar, I can't remember for sure) that orders to stop a sound were ignored. Sounds were queued to the channel instead of interrupting the previous one.