Tweener: 'alpha' not a property?

I have a custom class in which I create a large number of display objects pulled from the library. Each has its alpha set to 0 initially. Then a series of functions call Tweener.addTween to change their alpha to 1 and other such fun things.

(I did import caurina.transitions.*)

I also have a public terminate() function in this class that I call from the FLA when I click a button.

AFTER this class has been added to the stage – and AFTER all of these display objects got through their various tweens and become visible – I hit the button which triggers the class’s terminate() function.

Oddly I get this statement for each of the display objects:

## [Tweener] Error: The property 'alpha' doesn't seem to be a normal object property of [class WirelessPhoneIconFP] or a registered special property.

Meanwhile the objects disappear as they’re supposed to.

Any explanation for why alpha is suddenly not recognized, even AFTER Tweener successfully changed the alphas of all of these display objects?