before flex 4.6 on air mobile for android, if height dimension is not specified in a s:TextArea, the textArea auto-sizing, since flex 4.6 doesn't work.
Try switching back to the TextAreaSkin instead of the StageTextAreaSkin. StageText allows you to get native text input, but there are limitations as to how well it plays with the rest of the display list.
Thanks for posting this. I was having a problem where the text in my TextArea object would dissapear when testing on a mobile device. If I had a TextArea on the home view, it would display fine, but on any other view it would just flash for a second then dissapear. Switching the skinClass to the mobile textAreaSkin solved this problem.