A while back, my dad got an inkjet all-in-one scanner/printer. An Apollo, which are apparently rebranded HP things. And it was fine for a year or so, and then it developed a rather weird fault.
Every time you turned it on, it printed a test page.
I had a poke around, couldn't work out the problem. Tried resetting the printer to factory settings, removing it from Ubuntu and re-adding it, all that. Even looked in some sort of complex HP configuration utility thing in case he'd inadvertently ticked the "I have too much money, waste it all on ink, please" option or something. Nothing doing.
Secretly, I was scared that maybe it was an Ubuntu bug. Didn't want to say that to dad, though.
Anyway, time goes on; dad got used to printing a test page every time he turned it on, and started cutting the test pages in half and using the backs of them as scrap paper for taking notes on. Eventually, he got so annoyed by it that he bought a new printer -- a Kyocera Mita FS-1010, at my recommendation, because I've got one too and it's a brilliant little laser printer which works perfectly with Ubuntu and can be picked up for about forty quid on eBay. That's a laser printer, though, so it's only black-and-white; BW printing covers most of what he does (and all of the minuscule amount of printing that I do), so he only needed to turn on the Apollo when he needed a colour printout. At which point it would print a test page, print the page he wanted, and done.
A couple of weekends ago, after two years of this test-page nonsense, I thought: surely this must be fixable? Poor dad. I must try harder to fix it. So, up I went, turned on the printer, and it printed the test page. Which I then, for the first time in two years, actually looked at.
Turns out it's not a test page at all. When you put new ink cartridges in the printer, it prints one of these pages and then you're supposed to scan that same page; the printer uses it to re-align the printer heads, because it can see from the printout whether the lines are straight.
This "test page" explains all this, right there on the page, along with a set of diagrams explaining what to do for people who can't read. People who can read and just do not bother to do so are not catered for, however. So I scanned this page, and since then the printer's been stone-cold perfect.
There is a lesson here, but I don't know what it might be.