The past tense forms of karnaa include kiyaa (masculine) & kii (feminine). But I'm surprised that some native Urdu speakers say karaa & karii instead! Is this the influence of another language or dialect or simply poor Urdu?
It is definitely not standard Urdu. It is very possible that this is influenced by dialects or other languages. There was a discussion about it in the forum so please look for it and get back with a link as I can't remember now when and where it was.
We did this here! Although karaa / karii are not we would ever opt for but they are used by Urduphones and as mentioned in the linked thread, became accepted as an alternative before / around the time Platts wrote his "Grammar of Hindustani or Urdu Language" at the end of the 19th century.