A similar, but more severe, issue was reported back in 2010 and marked as completed: Small avatars for ignored chat users break chat's "people in room" display. A milder issue currently exists.
When a user is ignored and their small avatar is displayed in the "people in room" avatar grid, extra whitespace appears immediately below the row the avatar is in.
Changing the width of the browser window has no effect.
Chrome 41, Windows 7.