And how come the root changes from başla to başlı? I think we say başlıyor... Irregular as well?
The -i- of -iyor "eats" and replaces any preceding vowel.
So for example denmek "be said" and denemek "try" both give deniyor -- the first is den- + -iyor and the second is dene- + -iyor but the -iyor "eats" the -e- of dene- so you have den- + -iyor again.
The root stays dene- or başla- but the final vowel is "eaten" and you can't see it any more in the -iyor form.
İf any verb ends with a or e, you should replace it according to the 4-vowel way of the previous vowel. E.g. başla(mak) + yor becomes başlıyor
04-June-2019 "The day is not beginning but ending" – not accepted. Is it wrong?