search – The modified Twitter user name. Still in Twitter searches

If my Twitter account was @johnsmith and I had to change it to @johndoe, I would expect that searches done in the Twitter search entry for the old user name now show no connection to the new name.

On the contrary, if I change the nickname, wait a few days, then look for the old name, I see the many responses of other users tweeted on the old, and some of them – but curiously not all – have the new name. added to them now (they show as tweeted both the old and the new name, despite being dated before the new name exists).

Why would it be? Can it be avoided?