Yes, the common mynah does normally have tail feathers. We see a lot of them in our back yard. But this morning I saw one with an extra tail feather.
It's a large white feather, attached to the mynah's tail. I figured the feather came from a cockatoo - they're they only white birds abundant in this area.
And the feather was firmly stuck - I saw the mynah fly up to a tree a couple of times, and the feather stayed with it, more or less straight in alignment. I daresay the extra baggage must have either helped or hindered the mynah's flight, but I didn't see any evidence either way.
So, the question is: was it an accident, self-decoration, or did someone put it there? I would guess the former, although it seemed so firmly attached as to suggest the latter. Then again, has any ornithologist heard of a mynah decorating their own tail?