Robin35 (6/19/2013)
Principal server error log :2013-06-19 01:26:27.180spid27sSQL Server has encountered 1 occurrence(s) of cachestore flush for the 'Object Plans' cachestore (part of plan cache) due to some database maintenance or reconfigure operations.
proccache has been flushed/remove. It could because of server / database level configuration change or memory pressure.
Some times, if principal is running with low resources like cpu,memory (in your case of memory pressere) there is a possiblity of principal's low response to witness that may do failover.