Ion-radio with checked="true" does not work?

Hi,

I wanted to try the ion-radio component. Seems to work, but if I put one of my radio with checked="true", it does not check it by default when the view loads. Any thoughts?

<ion-radio value="byUnitId" checked="true">
  Unit ID
</ion-radio>

<ion-radio value="byMac">
  MAC Address
</ion-radio>

<ion-radio value="byUnitName">
  Unit Name
</ion-radio>