Hello,
I try today set the non standard subnet mask (255.255.252.0) in telnet UI. In the server settings I write 22 (other representation of the same mask). When I check xPort config there was mask 255.192.0.0.
The good news is that xPort work ok (the real mask was 255.255.252.0) only the text representation in Device instaler is wrong.

The DI version is 4.4.0.2