Adobe Air Android spark Label “transparency” on bitmap

The following works fine in the Windows Emulator.

On Android, I have a background image drawn via graphics.beginBitmapFill to fill a group. This draws fine.

When I put a Spark Label, Radio button, checkbox and other controls that have text, a faint background box is painted around the text. The color of the background seems to be based on some formula of the bitmap's colors. I have ensured that alpha's are 0, confirmed by having a breakpint in Spark TextBase when it fills the text background, the alpha is 0. If I change the background from a bitmap to a gradient fill, this "background box" behind the text does not appear. It only appears when the background is a bitmap. And there seems to be some transparency to this box as aspects of the bitmap bleed through. Is the text engine picking up that the background is a bitmap and doing something special to the text's bounding box? I've dug through the Spark source code (provided with the Flex SDK) and I don't know where to look next.

I'm using Flex 4.16, AIR 25. The Tablet is running Android 7.0. I have not tried on an iOS device as I don't have one readily available to me at the moment.

Any clues what I missing or doing wrong? Hoping this isn't a bug.