There is nothing wrong the registration of a single letter as a trademark, provided it fulfils its trademark function and be perceived as an indication of origin for consumers. This is not the case for the first, and one of the most used letters of our Latin alphabet, reproduced without stylistic effort.
This cancellation decision is also an opportunity to recall how important the nature and quality of the documents submitted to demonstrate the acquisition of the distinctive character of a trademark are. Yet another fine example of a biter being bit !