Performance issues with memcache module 6.x-1.13

A very large site we manage for a client was upgraded recently from the memcache module version 1.12 to version 1.13.
However, the result was less performance for this server that was humming alone happily with the older version.
The Munin graphs tell it all: look at the change at 12:00 noon.
Here is the CPU graph, showing double the CPU utilization on this sever.