A couple of years ago, after filing my return, they sent me a letter requesting copies of the 4 checks I sent to them, and they cashed, for quarterly estimated payments. In my cover letter back to them, with the copies of the checks, I asked them how could they possibly not have record of receiving and cashing the checks. Of course, this question was not answered when I got their "your documentation is satisfactory" letter.
Oh wow, you just refreshed my memory of a year or two ago, when they demanded proof I had paid my estimated payments each quarter. The ones I paid ON THEIR WEBSITE. They really are either completely inept, or willfully trying to avoid paying refunds. In either case it's unacceptable.