[tor-relays] [WARN] Your system clock just jumped 100 seconds forward; assuming established circuits no longer work.

[Zenaan Harkness]

My tor logs (running on Debian) are showing this warning:
[WARN] Your system clock just jumped 100 seconds forward; assuming
established circuits no longer work.

I tried running openntpd as well as ntp packages (debian), and both
display the same problem - once or twice a day I get this jump in time
of in the order of a couple of minutes.

Any idea why?

TIA
Zenaan