Hi Volker,
Leave to transaction will trigger the kernel to terminated the session in case ~singletransaction is active. Normally I would not expect to have this parameter in an ITSMobile application because there is no navigation menu that the user can use to jump to other transactions. Even if he could there will be no templates and therefore he would get a dump about missing templates.
If you are on release >= 7.31 and you use the ICF logoff service to delete the http security cookie you don't need to specifiy the sever and port. Please change it to
/sap/public/bc/icf/logoff?redirecturl=/sap/bc/gui/sap/its/<yourService>
Regards,
Dieter