I don't know if the rule is universal... I thought it applied to my native language only, maybe a few more.
"Long forgotten" only because I haven't written any formal (or even semi-formal) text in my native language for like 10 years. I use only German and English now and I don't think these rules apply there (I may be wrong tho).
Btw. my parents were also teachers and I was a good student
I'd rate my writing skills as very good (if I need to), maybe a bit rusty by now. But nowadays, all my writing in Slovak has shrunk to instant messaging without any rules and even without any diacritics (no accents, carosn, circumflexes, umlauts, etc.).
Good to know there are people who still obey the rules tho