can not create a new domain with "_" says domain name invalid

[arisd]

Well... First bug I noticed in Plesk v8.1.1.

When I try to add a new domain "agencija_ultras.si" plesk says:

Error: Domain name is invalid.

But domain name IS valid!!!

Anyone knows the solution to this problem or should I write to Plesk and report a bug?

Thanks, Aris.