[Embed(source='font.ttf')] suddenly failing in AIR 13.0

Hi all,

I have an app for iOS and Android that we've been testing for about 6 months with no problem.  It uses Embed code to define 5 different fonts used throughout the app, like this:

[Embed(source='fonts/Feijoa_Medium.ttf', fontFamily="_Feijoa", fontWeight=FontWeight.NORMAL, advancedAntiAliasing="true", embedAsCFF="false")]
  public static const FeijoaClass : Class;

// Sometime later
Font.registerFont( FeijoaClass );

This has been working perfectly in AIR 3.9

I recently upgraded the AIR version to 13.0 (Edit: also happens in 14.0) and first received this error message:

Build failed: Warning. The constant 'FeijoaClass' was not initialised

On a whim, I changed the variable to private static var like this:

[Embed(source='fonts/Feijoa_Medium.ttf', fontFamily="_Feijoa", fontWeight=FontWeight.NORMAL, advancedAntiAliasing="true", embedAsCFF="false")]
  private static var FeijoaClass : Class;

The project now compiles, but I get the following run-time error on the Font.registerFont call:

[Fault] exception, information=TypeError: Error #2007: Parameter font must be non-null.

And sure enough, all my embedded classes are null.

The path to the font is correct.  However, another weird thing is that if I deliberately change the path to the font to be incorrect, I do not receive any sort of error (I'm sure i used to in AIR 3.9 if the path was incorrect).

Any ideas?  Scratching my head at this one!