This appears to break the styling of title bars on at least beta SE sites. At load, the Custom Edit Reasons dialog pops up, and on closing this it appears that the topbar is using position:fixed. While I appreciate this, it would be good if it didn't obscure the top part of the title bar.
(UPDATE: this happens on full sites as well - StackApps just fell victim)
Without 'Fix topbar position' enabled:
With it enabled:
