This can be due to the views.dat getting reset. I also remember someone putting up a post similar earlier and a response saying it was a bug in SP. I don't remember whether it was the same SP 13 that it was about or not.
Check the updates in SP14, that may tell you whether it was a bug with 13. The filter can get lost if the Cache files get reset.
Hope this helps...
Modesty is good!! But remember, all your life other people will try and take your achievements away from you, don't make it easy for them.