IRS Employee Tax Compliance Event

In 2017, while on involuntary furlough from my employment at IRS (...they frequently lay off "seasonal" employees when they run low on money, with the excuse that there's not enough work...) I got a letter saying that my 2016 taxes had not been paid when due.
I had filed an extension, reasonably expecting a refund because I'd always gotten a refund, but also including a small payment just in case. The reason for the extension was having to work through the taxes during the year of divorce, and it was not like Kris was ever going to help with providing the information I needed to do that. Also, I'm sure I was just avoiding the issue since divorce is not something one enjoys cleaning up after.
Anyway - I have used a spreadsheet to calculate my taxes for years, because my first experience with an early version of Turbotax was quite negative and the one time I went to a preparer (just after buying this house) was quite negative - they didn't figure out anything I didn't know about.
However as luck would have it, there was a defect in my spreadsheet - just one formula for calculating self-employment tax - so I owed. I paid as soon as I got the notice and then forgot about it.
We'd been told in training that the IRS checked up on this, and sure enough: they did. I wrote back with an explanation and they responded saying it was nontrivial and they were referring it to another unit which would contact me.
This worried me. Could I lose my job? Maybe, although I was not that worried since we're chronically understaffed. Probably I would just have to go through some additional training since this was my first time, and I don't mind more training.
Eventually somebody called me to talk about it. Since I was on furlough, I considered refusing to talk with them until I got back to collecting a paycheck from them and could have union representation. I did ask about union representation, and the caller promised to have a union guy on the line when he called back. When he called back there was no union guy; I was not terribly surprised and decided, what-the-heck, let's just get it over with. I don't remember how many calls there were but I guess my story checked out. The caller asked why I had eventually gotten a refund and I explained that after paying in full, I amended to do something with my deductions. I doubt that was ultimately determinative of the outcome but I was prepared to argue that I had not actually owed very much at all - even at its maximum my debt was under $2000 and I doubted they'd fire someone for owing that little and paying promptly.
Anyway, I was told this was being referred to my management for whatever further action they would take. I heard nothing more. Maybe Seattle AM was uninterested in taking me off the phone for training in how to file my taxes.
The process was disturbing but it worked to just respond calmly and get it over with. I suppose it's nice to see that some checking is done to ensure federal employees aren't screwing around with their taxes; it would be nice if the same would apply to our political leaders. But that's another story.