If multiple modules all have the same adjusted API level, the error message isn't helpful. API levels are pulled up to the minimum supported API level for the ABI, so if the module accidentally has both an API 19 and API 21 library for a 64-bit ABI, it actually has two conflicting libraries for API 21.

This is an error in the package so there's no bug here, but we could probably diagnose that case and provide a useful error message to the user.