If I understand correctly, if the option "Persist selections on deselect" is unchecked, upon deselecting the corresponding field the parameter should be reset (blanked).
If this is the intended behavior, then it seems it is not working.
In the attached example, having the option checked or unchecked seems to have the same effect, once the parameter is filled in, it will only be updated when a new record is selected and nothing happens if the selected record is unselected.
Thank you so much for pointing this out, I've updated the extension to work as intended. Bonus points to you for finding a bug!