It might be searching inside of archives. I don't think you can control that setting from buttons right now and I think instead they inherit whatever is set in the GUI when you use the button.
If it's not that, can you post a screenshot showing the find panel setup that is fast? Maybe there will be some difference between the two which we can spot.
BTW, you might need to put quotes around the {dlgstring|...} part if you want to be able to search for names containing spaces.