You should read the documentation of
PropertyGrid[
^] class...
'click' event is not an even of the line (property) but the control itself. The reason id does not fire for the value-side, is that there is an other control there, that gets the focus and handles the event, while at the text-side it is the control itself...
If you want to follow changes of properties via PropertyGrid you should follow the
PropertyValueChanged[
^] event...