The bug

The text field for changing the profile name in the "Change profile name" section of https://www.minecraft.net/en-us/profile appears to always update the error state (e.g. whether profile name is invalid) when an availability API response is received.

When you type quickly (or have a bad internet connection) it could therefore happen that an API response updates the error text despite you alreading having changed the entered name in the meantime.

Reproduction steps

1. Open https://www.minecraft.net/en-us/profile
2. In the text field for changing your profile name, hold down the a key for a few seconds, then quickly afterwards press the Space key
   For a short moment the error message says "Your profile name can only include letters, numbers and underscores." before switching to the outdated (and incorrect) "This profile name already exists."

The same also can be seen where after quickly inserting an invalid character behind a valid name, for a short moment the error message says the name is invalid, but then being cleared and the website (erroneously) claiming that the name is valid.

Suggested solution

When receiving a response from the API, verify that it is still relevant for the current input.