When I use an exclamation in the filter like !*.txt to exclude txt files, it always seemed like it came up in the results. What I "failed" to realize was that txt files will still appear in the list while the compare is going on. Once the compare is completed, then it removes it from the results pane.
I have only used this in my work experience when comparing tens of thousands of files, so I never let the compare complete before fully "testing" the exclusion. I have to say this was quite confusing. I have only realized this weeks later when I actually left it running due to other distractions and realized no txt files were in the results.
