Interestingly that someone else is affected, (RTC issues causing possible history log corruption - #4 by mabnz) had already feared that the local network structure caused the problem. I have now done some more research and it is no coincidence that the time jumps to 2036 (RTC rollover in 2036):
NTP uses an epoch of January 1, 1900 so the first rollover will be on February 7, 2036.
Source: Year 2038 problem - Wikipedia
In this thread the cause is mentioned:
I have seen in some case that NTP can and will reset a computers time to the
year 2036. this seems to be the case when a machne senses a NTP time packet
that contain the time 0000000000.0000000000.
Source: http://compgroups.net/comp.protocols.time.ntp/-ntp-sets-time-to-year-2036/205808
Perhaps another more precise solution would be not to allow this time? Even in 2036, this time stamp will be valid for a maximum of one day.