Can't change deployment key to SSH key.

After using the same deployment key for various repositories I decided to use the same key as SSH key to avoid adding this key for each repository.
However when I try to add the SSH key I receive the message “Someone has already registered this as a deploy key.”. I checked all my repositories, but none have a deployment key registered with the same ssh key.
Maybe Bitbucket is checking a deleted repository for any deployment keys?