individual_prefix option value can only be integer

In civicrm/admin/options/individual_prefix you can edit the individual_prefix options. I wanted to make them more friendly for coding purposes so I changed the values from numerical (integer) to strings, which is allowed there (no warnings or errors). The problem arises when you want to use the API to set or change an individual's prefix_id. It will error out with the message: prefix_id is not a valid integer. Apparently the API does not count on option values different than integer number strings.

If this not accepted as bug then bold written documentation seems polite, because this cost me a lot of time to discover.