The Security and Countermeasure Guide* said about the Accounts: Administrator account status local policy settings:

Under safe mode boot, the Administrator account is always enabled, regardless of this setting.

Yes, the Local Administrator Account is enabled under safe made boot, but the Account is disabled checkbox is still checked. You can uncheck it, of course.

Also you can uncheck it if you are logged under Domain Administrator account.

*Security and Countermeasures Guide.pdf, Version:  1.2, Date Published: 10/19/2004