Accounts with special characters don't get changed when migrated

The bug

When an account with special characters in it gets migrated, it won't change the name so the special characters are not removed. Known special characters are: hyphen(=-), exclamation mark(=!), space(= ). This happens to accounts with accents, can't confirm this but a source has told me so.

Note: The creation of these accounts is not a bug as in the Alpha days of Minecraft, you were able to create these. But, nowdays, people use advanced tools to mass scan the API, find names, and crack these accounts.

Example

glenn-stroek
Awesomeness!!!(link)
In Shadow