User Changes in AD stuck in people picker

My organization recently changed the user naming policy, removing spaces from user names replacing them with dots.

For the most part everything works fine with this change, however, the old user name appears to be “stuck” in the dropdown in the people-picker controls used in lists.

I’ve found that if I explicitly type in the proper name (with the dot) it works fine…but it still brings up the old name with the space between names as a possible selection.

When the name with the space is used it presents an error: “The user does not exist or is not unique.”

How can I make the old name go away?