gae share session across modules in dev mode

I've and gae application (gae 1.9.14 and guice 3.0) consisting of two modules with sessions enabled. In local development those modules get deployed on different ports. Each time I initially access a different module (even with an existing JSESSIONID) a new session (with a different JSESSIONID) gets created. I'm therefore not able to share my sessions across modules.

Actually I don't know if this is a gae related problem but any hint would be appreciated.
cheers