Deleted answers appear in the global inbox. The same way it used to happen with comments
Also the number of answers takes the deleted ones into account.
This appears to have been caused by some transient network issues earlier today.
There haven't been any changes around the inbox in quite a while.
Aren't the Inbox links for new comments to (deleted) answers odd as well?
Like today I got the following link for a notification of a new comment on an answer:
(For new answers, the URL in the Inbox is always a proper URL of the second form.)