When the L2 switch installed, it inserts a few flows into the network. These flows are picked up by the stats manager. But the stats manager keeps interpreting these flows as new flows with each collection request/response, Thus, the number of "discovered" flows i in the oper space grows until the controller runs out of memory.

This is being addressed by Gerrit https://git.opendaylight.org/gerrit/#/c/11598/.