[flexcoders] DateField - minYear and maxYear - don't work if they contain calculated value?

[flexcoder2008]

I have a DateField and if I set the minYear or the maxYear property to a value 
directly, everything works great.

eg.  

<mx:Datefield maxYear="2009" minYear="2000"/>

But if I want to use a calculated value in there, it doesn't work.  I can 
navigate past this value. 

eg.

[Bindable]
var year:int = new Date().getFullYear();



<mx:DateField maxYear = "{year}" minYear="{year - 10}"/>


Why is this? Does anybody have a workaround for this?