Character set messed up on password protected page login

The topic pretty much says it. Here’s the page: http://skytry.fi/wp/tuote/yritysjasenyys/
On every other pages those strange exotic letters load just fine.

I tried replacing the text with a function. Got a little different result. It replaced the “Ä”s and “Ö”s with those little ascii question marks inside a diamond.