Kwallet password prompt (and possibly ksecretservice too when implemented) should raise its window on top of others for security reasons.
Test case and one of posible scenarios:
Suppose you are chatting (irc for example), and start kopete (just an example), you login with it, but you are still chatting. There are times when that password prompt window goes behind and without focus, but you type password and hit enter.
You think you are typing in password prompt (if you are not paying much attention) but instead you are sending your password somewhere...

I think that kind of scenarios should be avoided to have more security. The pros are more than the cons, because if you type anything in password prompt, any side effect will be produced (which the opposite can be dangerous).

Reproducible: Always