Redis session locks

Hi
I'm using the Redis session handler, connecting to AWS elasticache Redis over TLS (non clustered).
On the whole this works fine.
My application is very ajax heavy and i have noted the use of session_write_close() and am using this accordingly where appropriate.
What i've noticed is that if this isn't used, then the sessions get locked correctly, but after the 30 failed attempts, it then seems to clear the session data completely rather than just ignoring it or ending the script. in effect, logging my users out of any other tabs they're in.  Is this correct behaviour?  and if so should it be?
I would expect the lock to fail but the session data to remain, not get overwritten by an empty value.
Am I missing something here?
Thanks