When a candidate's nomination is withdrawn, their username is removed from the menu that lists candidates to be added to the ballot (on desktop). However, on mobile (responsive mode), the dropdown still shows the users whose nominations have been withdrawn.
On the following side by side screenshots of the current Stack Overflow election, only 5 candidates are listed on the menu on desktop, while 6 are listed in the dropdown on mobile:
(Username(s) were anonymized to not make it about certain users)
Note: selecting the candidate's username from the dropdown does not actually add it to the ballot, but it still should be removed for consistency with the desktop view.