Mask parameter in Windows Real-Time Target UDP Receive Block

I am using Simulink Windows Real-Time Target to process data received via UDP. For the sake of modularity I hide the UDP receive block as well as protocol checking and unpacking are inside a subsystem.

Now, it would be most helpful to also design a custom mask for said subsystem in order to adjust for example IP-Address and Local Port number. However, when I try to insert mask or even workspace variables in any field of the UDP block's mask, MATLAB crashes and the Windows Target is unusable (can not connect to Target) until I logout from my windows account.

Please advise a workaround.

Best regards, Arne