Logging slow stored procedures caused the slow log to write 
very large lock times. The lock times was a result of a 
negative number being cast to an unsigned integer.
The reason the lock time appeard negative was because 
one of the measurements points was reset after execution
causing it to change order with the start time of the 
statement.
      
This bug is related to bug 47905 which in turn was 
introduced because of a joint fix for 12480,12481,12482 and 11587.

The fix is to only reset the start_time before any statement
execution in a SP while not resetting start_utime or
utime_after_lock which are used for measuring the 
performance of the SP. Start_time is used to set the
timestamp on the replication event which controlls how
the slave interprets time functions like NOW().