Currently in the blocking mode, the search is immediately performed when you check/uncheck a box. This makes it harder to select many checkboxes at the in a quick succession and performs wasteful search many times.

"Debouncing" is performing an action after some timer expires. I propose to test first a value of 0.5 seconds. It basically means, that when a checkbox is pressed, you reset timer to 0 and wait for 0.5 seconds before you start a search. Each click resets this timer, so the search only starts after 0.5 seconds of inactivity.

It is a good idea, I'll certainly consider it. Currently you can right-click on the item selection box to clear the selection, then check/uncheck as much as you like without any obstacles. Ideally I was thinking of having shift-click on the checkbox not start a search, but that isn't possible in the current API and many people wouldn't know about it anyway. I think your solution is good.

Done!