Hi - we experienced the same issue with one of our apps last month. Our work around (it's not great) was to do this:
<s:TextArea skinClass="spark.skins.ios7.TextAreaSkin" ..... This created a weird blue hue around the 'prompt' text - but fixed the sliding position issue..... -- Sent from: http://apache-flex-users.2333346.n4.nabble.com/
