Question about login-logout function in EPM

I set up two phones as extensions 9998, and 9999, and two phones to match, and all comes up OK. However, if I try to log in one phone to the other phone’s extension, the system immediately restarts the second phone, and erases the configuration completely, even the config server IP address. Does this mean that it is not possible to have two phones on the same extension? I have had this capability with the Aastra scripts, using device/user mode, and my customer will not be satisfied if I can’t provide this capability on an updated server…

Is there a solution?