Writes via memcached server cause UnknownOperationException

We're using the stable server version (http://infinispan.org/download/) as a memcached replacement in a PHP application. When we're writing keys (or values) with different sizes via memcached, we encounter the following exception:

{{17:14:42,531 ERROR [org.infinispan.server.memcached.RequestResolver$] (MemcachedServerWorker-8-1) ISPN005003: Exception reported: org.infinispan.server.memcached.UnknownOperationException: Unknown operation: }}

When the exception occurs, the data is not stored.

We're currently closing and reopening the connection after an error like that occurred, but it's slowing down the data transfer quite a lot.

The bug is not only related to the server, but happens with the embedded version of infinispan, too.