Mikolaj,
Thanks for the problem report! I will appreciate if you provide more specific description for problems you encounter: a) what you do,

what you observe as a result of your actions, c) what you expect to see.
In this case, I guess you mean that default values for severity and priority are not preset in the new bug form. Agree, we have such a problem and we're working on it:
http://bugs.deskzilla.com/show_bug.cgi?id=100
Cheers,
Igor