First off, good job on a user-friendly utility for testing TWAIN drivers. For a long time now developers and users have needed a good way to know which DS's are following the specification and which ones fall short. I hope your utility can become the gold standard.
Anyway, I tried Inspector Twain 2.0.0.3 on a DS that my company is currently shipping. It reported one error that didn't make sense to me. For ICAP_PIXELFLAVOR it reported "MSG_SET failed even through [sic] the driver indicates it's supported". I stepped the code and found that your utility is using an enumeration when setting the pixel flavor. I believe this is a bug since the 1.9 specification states that you can GET the pixel type as an enumeration or a single value but it must be SET using a single value.
Please let me know what you think about this. Once this problem is resolved I'd like to submit my company's products to your database.