Thank you for the speedy reply.
I did some more testing with your comments and I found the following:
If I send 138 as the first command after power-on and after that I send either an MVP or start my stand-alone program, I do get the "target position reached" messages.
However, if I first start my program and THEN send 138, I never get the "target position reached" message. Not even after I stop/reset the program and send 138 again.
In this situation there seems to be no way to get it to work other than cycling the power.
Also, this would mean that I cannot use the "auto start mode" (global parameter 77).
P.S. you state that the type parameter in cmd 138 should be 1 to enable, but the firmware manual states that the value of the type parameter doesn't matter. Also, the manual says that the request message requires the motor number, and not a bit mask.