You’re right; Aspose.Words for .NET currently throws following exception upon comparing these particular Word DOCX documents:
Message=Unable to cast object of type 'Aspose.Words.Paragraph' to type 'Aspose.Words.Run'.
For the sake of correction, we have logged this problem in our issue tracking system. The ID of this issue is WORDSNET-22623. We will further look into the details of this problem and will keep you updated on the status of correction. We apologize for your inconvenience.