Bug in kmail 3.1?

I just found what looks like a bug to me: i switched off the "unread column" and "total columns" under the "view" menu in kmail 1.5 (with kde 3.1), and they go away as expected. I switched them on again and they do not reappear. I try switching them on and off with no result, the columns would not come back. I give up and start reading my mail, and when i resize the lateral window, the columns come back! Am i missing something or this is not how the whole thing is supposed to work? fred