Hello Andrei,
I didn't had the time to handle this upgrade to JBoss 7 this last few days. Indeed I use my dummy login module in this way, without this option:
<module-option name="password-stacking" value="useFirstPass"/>
for it.
But this option is enabled in my real login module and the multiple call to EJB problem persists even when calling methods remotely or locally from a war.
The problem with multiple calls to the EJB as I understood it will be solved in 7.1.2 version.