When I worked as the lead designer on Microsoft Money, I eventually came across its scary basement: the elaborate checkbook register control for viewing and editing account transactions. This register control was first created around 1990 by legendary Microsoft engineer Doug Klunder. To get the most performance out of the PCs of the day, I believe he had the register itself more or less directly read and write transaction data from disk. In this capacity, this specific UI control was entirely and solely responsible for validating all transaction data; there was no separation between presentation, business logic, and on-disk representation.

Yup, sounds like MS to me. Bashing aside:

To prevent a critically important aspect of your UI metastasize into a scary basement means investing time in refactoring as you go, and this means moving more slowly that you would like. UI changes need to be evaluated in terms of the degree to which they compromise the solidity of the foundation.