kmail: searches don't work

After sometime using thunderbird, I went back to kmail. I noticed that searches (File -> Find messages) don’t work.
To begin with, the box to indicate where to search (in a specific folder or in all folders) has disappeared. Then, after pushing the button “Searh” it just blinks, finds nothing and is ready for another search.

Has anybody else experienced this? Is there any solution?

Thanks.

I forgot to say: kmail 4.7.3 Opensuse 12.1