Cm_RedisSession module disabled when config cache is enabled

[PeterGLake]

I'm configuring my v1.9.0.1 site to use REDIS for session storage.  I've enabled the module by setting active to true in module XML.  What I've found though is that the module is not used when the magento config cache is enabled in cache management.  The sessions are being saved in Core_Session.  As soon as I disable the config cache, my session is lost and I have to login the admin site again.  I can then see that the session information is being written to REDIS instead of the database.  

There are no errors being thrown and the redis_session log is not written too unless the config cache is disabled.  Weird!

Anyone got any ideas?

Thanks.

P.S.  Sessions are stored to redis if I disable memcache for 1st level caching.  

[PeterGLake]

Turns out that the Flush Cache button wasn't clearing the memcache cache and hence it was using the cached version of the modules XML file.  I had to telnet onto the memcache instance and execute a flush_all.  No idea at this point why the button doesn't work.  More investigation required.