The scenario is:
This is different than clicking on the Windows "X" to close the session. TPX does terminate all active sessions and user can subsequently sign on.
However, when the session just drops from Wired -> Wireless, no errors are seen yet users cannot sign on again.
When the emulator is closed with the X, VTAM is aware that the connection has closed and, in turn, TPX is also aware.
When the wired connection is disabled (wire is pulled), the connection is still considered active by VTAM since no 'action' is requested by the 'user'.
In other words, when X is selected, this is a user 'action' and is passed to VTAM. Pulling the cable is not a user 'action' that is passed to VTAM.
When the user reconnects with a wireless connection this is a different network path, with a 'new' session from VTAM perspective.
Since the wired connection is still considered 'active' for all sessions previously started, VTAM correctly returns an "Already logged on" message.