PVR – $INFO[VideoPlayer.StartTime] is counting back 2-3 times every sec

if $INFO[VideoPlayer.StartTime] or $INFO[Player.StartTime] is used together with Live-TV (VDR here) the starttime is counting back 2-3 times every sec. It should not differ, because the starttime is always the same.
Is this a known bug or what can be done to get the starttime for the actual playing program in LiveTV?
Thx

NextStartTime etc. are working … btw.