Tax suddenly being applied when it should not

[Brewhaus]

In the past month we have started to see tax applied to orders that do not fit our criteria. This was never an issue before, but recently it has become a problem, but only on a few select customer accounts. We have double and triple checked the tax criteria (tax based on shipping address, only to TX). The only change that we made somewhere near the time frame of this starting (and we cannot say that it was definitely at that time, nor that they relate- but it was the only change made) was to (unsuccessfully) try to delete the anonymous users that are still hanging around in the db.

Does anyone have any thoughts??