Avisynth and Incorrect frame rate

I frequently encounter situations, when avisynth in VirtualDub preview showed all OK, but on saving video it doubles frame rate!

Please, consider small sample:

clock.avi

AVI file, 32496 frames, 57:30.90, record for system clock, from 16:32 to 17:30

clock.avs

Dummy AVISYNTH script (DirectShowSource("clock.avi"))

Download example archive (≈200Kb)

Файл:Clock.zip

If we open clock.avs in VirtualDub, and jump to frame at time 10:00, we see 16:42.

If we save the video (by VirtualDub, the codec does not matter) open saved video and jump to frame at time 10:00, we see 16:53.

What is going on? Is it bug or some feature?