Reports using custom value list fails after Find request
I have a to do list with items assigned a category from a custom value list for priority, High, medium, low. I created a report grouping the items by priority - it works UNTIL I perform a find, after that, the groups just disappear. I have gone for Show all records. Although all records appear in the list, the categories no longer do. Why is that and what can I do to prevent it happening?