I've run across this a couple of times, and maybe it's something internal to mantis tool.
Steps to create this:

1. Go to "My View".
2. Select "Reported by Me"(for example) in the View Issues buttons.
   [this takes you to the View Issues tab, displaying the selected sort]
3. Then go to "My View" again. Next select different button (for example select "Resolved") in the View Issues.
4. Click on "Category" (for example) to sort based on the column. (The place you click 'Category' in has been shown in the attachment.) >> The displayed information has reverted to a previous search.(The interface reverted to "Reported by Me" from "Resolved" and the sort of new-jump "Reported by Me" is correct )