Numeric-but not numeric enough+example

I added +Hours to the structure of card type "Task", entered the rules to change the default of all +Hours to type Number, and recieved the error:

CONTENT: '.25

' is not numeric

It does not matter what appears in the card, or if the card is being originated and has no content of any kind. Still " ' is not numeric." 

I even erased everything at the HTML level. Still ' haunts me.