Still getting 'calcru: runtime went backwards'

I'm still often getting calcru output.  This is with
FreeBSD anh-thu.NUXI.org 7.0-CURRENT #44: Tue Jun 27 09:30:45 PDT 2006 amd64
I'm using the default time source (ACPI).  What's the latest theories of
the cause of this?

calcru: runtime went backwards from 542 usec to 271 usec for pid 142 (adjkerntz)
calcru: runtime went backwards from 48 usec to 35 usec for pid 24 (usb2)
calcru: runtime went backwards from 27 usec to 23 usec for pid 21 (usb0)
calcru: runtime went backwards from 5267 usec to 2633 usec for pid 7 (acpi_task_2)
calcru: runtime went backwards from 4132 usec to 2066 usec for pid 6 (acpi_task_1)
calcru: runtime went backwards from 226 usec to 159 usec for pid 15 (swi6: task queue)
calcru: runtime went backwards from 46257 usec to 45630 usec for pid 4 (g_down)
calcru: runtime went backwards from 5380 usec to 5271 usec for pid 1 (init)
calcru: runtime went backwards from 1709697 usec to 1131474 usec for pid 1 (init)
calcru: runtime went backwards from 503 usec to 251 usec for pid 0 (swapper)
-- 
-- David  (obrien_at_FreeBSD.org)
Q: Because it reverses the logical flow of conversation.
A: Why is top-posting (putting a reply at the top of the message) frowned upon?