Investigating, I created this capx that seem to spot the problem.
TiledBackground (TB) textures are not power of 2.
Launch the preview it works. (even in webgl)
Put an instance of text object in the layout, preview.
Firebug raises the same error as I reported earlier.
Put an instance of button object instead, preview.
Firebug raises an error inst.drawGL is not a function (l.1619 in preview.js).
The screen is all black with the button clearly visible. Tilebackgrounds and sprite are not displayed.
It seems it has more to see with the upper 2Dcanvas Ash uses for text rendering than with the tiled background.