I'm using several saved searches. Whenever I switch from one of these to "New Serach", Toodledo shows (after several seconds of contemplation) a list of all completed and uncompleted tasks. (Sometimes Firefox additionally shows a message saying that a script doesn't react anymore.) Then, I have to choose "Modify" so I can create a new search with the criteria I want.
I think this bug appears only once after every login and it is a rather new one (first appeared several weeks ago).