RTC Clock - Unexpected Time Changes

[panda]

GPy 1.18.2.r7

I am setting my RTC clock after connecting to Internet:

rtc = RTC()
rtc.init()
rtc.ntp_sync("pool.ntp.org")

Te above is successful. However, after some period of time the unix time returned from time.time() is incorrect. When this happens it is always push into the future 3-4years.

Does anyone else experience this? Calling rtc.ntp_sync() will clear it up, however why does it change in the first place?