Cannot enter Host name in format of this@that@other

Running WinSCP 6.3.1

Using site manager to enter a new or edit an existing site, I cannot enter a host name which is in the format this@that@other. The screen strips off this@that as the User name and leaves only other as the Host name. I can find no way to edit this such that I can enter this entire string in the Host name, and an unrelated string (e.g. my_user) as the User name.

Is there a workaround to override this behavior? Maybe an option to shut it off?

Thank you!

How did you get to the format this@that@other? Valid characters in hostname are only letters, digits, hyphen and dots.