Mobile AIR apps replace TextInput and TextArea with StageText by default. StageText allows access to native input behaviours (copy/paste, predictive text etc).
To remove this functionality, explicitly define the skin classes for TextInput and/or TextArea:
<s:TextInput skinClass="spark.skins.mobile.TextInputSkin" />
<s:TextArea skinClass="spark.skins.mobile.TextAreaSkin" />
This way StageText will not be used and you wont get the annoying paste option popup