Str82u - 2:08 am on Jan 12, 2013 (gmt 0)
I've had it happen after 2 years of a dot net being forwarded to a dot com. Decided to play with something on the dot net figuring "Hey,, it's been two years, no external links to the dot net". The SERP for a term had both the dot com and dot net together at #1 and #2 and it showed the actual content from 2 years back with the old page name that only exists on the dot com now BUT the cache was the actual current content. Switched back to 301 the domain to dot com.
This occured about mid year 2012