Gradle version: 2.1
Android gradle plugin version: 0.13.1
OS: MacOS

STEPS TO REPRODUCE:
1. Add a string to res/values/strings.xml
e.g. <string name="app_name">SimpleTest</string>

2. Add a product flavor which overrides this string:
productFlavors {
INT {
resValue "string", "app_name", "SimpleTest INT"
}
}

3. Execute:
gradle assembleINTDebug

EXPECTED RESULTS:

Build succeeds and the app is named "SimpleTest INT"

OBSERVED RESULTS:

Build fails with error:

:SimpleTest:mergeINTDebugResources FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':SimpleTest:mergeINTDebugResources'.
> /Users/xyz/AndroidStudioProjects/SimpleTest/SimpleTest/build/generated/res/generated/INT/debug/values/generated.xml: Error: Duplicate resources: /Users/xyz/AndroidStudioProjects/SimpleTest/SimpleTest/build/generated/res/generated/INT/debug/values/generated.xml:string/app_name, /Users/xyz/AndroidStudioProjects/SimpleTest/SimpleTest/src/main/res/values/strings.xml:string/app_name

ADDITIONAL INFORMATION:
When I add a resource file via a sourceSet for this build flavor instead of using resValue, I can successfully override the app_name.
I think setting a resource with resValue should behave the same as when using a sourceSet.