I do not see anything "blocking" the filter box.
A "blocking" would mean to me that no further input is ever possible.
This is not the case as functions are immedidately available after another click into the filter box.
The behaviour that you describe applies to any combo-box. As soon as you change to edit mode, mouse wheel scrolling is disabled.
You can recognize the edit mode that the selection disappears and the keyboard cursor appears.
If you click into that combo-box again, the mouse wheel functions are available again.
You may test this behaviour e.g.with any field in the tag panel where you cannot scroll to <keep> and <delete> once you have started editing. You would have to click into that field again or press Cursor down