I'm not convinced. set_property will automatically notify for the property you are setting, it wil not notify for the property corresponding to the previous image type.

Created attachment 309100 [details] [review]
pathc

You are right.

What about this instead:
 - remove the icon_helper_clear that's not needed
 - make it more explicit that we are notifying another property and avoid extra notifications if the image type is the same

Review of attachment 309100 [details] [review]:

other than that typo, looks good to me

::: gtk/gtkcellrendererpixbuf.c
@@ +322,2 @@
 static void
+notify_old_storarge_type (GtkCellRendererPixbuf *cellpixbuf,

arrrr, you got an extra r here: storage

aye, captain!

Patch amended and pushed.