evidently what becomes standard gradually changes. i believe you can see this in construction of the past tense (perfect tense) of verbs in Polish/etc vs Russian, where Russian just uses the grammatical past participle as if it were the simple past tense.

Speakers of English in the Americas make this same substitution, which sounds like a mistake to those who speak in the version of English taught in schools. They will say "i seen that" rather than "i saw that", for example, just as would happen in Russian.