I have noticed (v3.5.5 and possibly earlier) that the image for the Retire / Switch Sides button disappears in the editor; making it appear as though a button icon has not been defined. The button icon still appears on the game’s toolbar.
This is fixed in VASSAL-3.6.0-SNAPSHOT-cab4c3c and later. vassalengine.org/builds/
Agreed, Tests out in snapshot VASSAL-3.6.0-c7b63d3.