When adding a google map view (I extended a MapView, used the xml editor to add it to the Activity, and added my google maps api key to the layout xml file manually)
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For what its worth...
My experience is that I got this in the UI Designer, but it did not break the build. I assume it is an Eclipse / Android SDK bug.
My app has been working perfectly on the store until I upgraded my SDK to version 20. It leads me to believe this is something to do with the SDK.
Of the various answers to this question (and duplicates) I found, none of them helped:
not changing the target SDK
not clean & build
not declaring a style manually
Finally, these questions are all duplicates (and mostly useless as confirmed by Ewok):
I tried to point this out to the moderators but I was ignored...