[palosanto]

So if you are selecting favorite A, then updating its settings, then you long press favorite B and select "Update to current settings" without ever actually tapping it to switch to it, it will just favorite B to match favorite A.

Does updating a favorite includes changing the actual stamp image or only the properties?   That's what happening to me ...

I can't think of any other reason the sizes for the favorites would impact each other. If you select favorite A at size 12, then tap update to current settings, then you tap Favorite B which is size 14 and tap update to current settings, nothing should happen. It definitely should not change favorite B to size 12.

I was talking about the actual Stamps library, not as favorites.  If I select a stamp and change its size, the other stamps size also change. That's why their corresponding favorites change too.

Sorry ignore the last sentence "That's why their corresponding favorites change too."  

EDIT  Ok,  I see that the key element here is to select the favorite before "Udating to current settings".  Selecting the favorite also selects it in the Stamps window and will get the properties from it (including the icon itself).
However, the problem described above about the size changes on one stamp affecting all stamps still remains ...  (I'm talking in the stamps window, not the favorites)