To reproduce:
-add an AnchorPane
-add a Button to it
-try to set MinWidth to -1 (which is a value of USE_COMPUTES_SIZE constant) Inspector accepts the value but didn't change it to constant name --bug (if user unselect the button and then select it once again the value will be replaced with constant name)
-try to set MinWidth to "-Infinity" (which is a value of USE_PREF_SIZE constant) --it's impossible as a side effect of rule that prohibits letters in fields for int values --bug