other language symbols

I have textboxes and information in my forms written in swedish. Some of the letters used are: å, ä and ö.

Very frequently these letters get changed from standard swedish letters to a bunch of incomprehensible symbols.

I then have to go in and rewrite the textbox. This alleviates the problem for a few days before it happens again.

Is this a known issue? Can I do something to prevent this?
vilhelm