Ask HN: My HP 400 printer switches the letters on some fonts

Hi, my HP m451dn (400 series) laserjet printer recently started to switch letters, usually to Polish (I'm Polish too, so that's nice) on certain fonts, i.e. only on those which are monospaced. I print a lot of text in Times New Roman and other serif fonts, but when I print my songbook which I maintain in Courier/Droid Sans Mono it prints it with broken letters. Instead of fis I get fiś, instead of Jezu I get Jezż.

Yesterday I found that if I switch font to Consolas I get correct letters. I think this might be due to text being sent to the printer without font, but common substitution of Droid Sans to Courier Postscript happens, but I can't find an option to turn it off. Do you think this is broken memory, or maybe I should reflash it? I googled a lot of hp support pages, but nothing found