Sorry for the delay in replying while we looked into this issue.
This is an inconsistancy in Resident Licensing which applies to normal online activated licenses which can be set to expire N days after activation. Since Resident Licenses are not activated there is no way to tie this date dependancy to an unfixed marker.
The solution, and correct way to achieve this result is to set an expiry date when "Creating a license from a SKU" option. Set the SKU start date to a date in the past (for example 2001-01-01) and set the expiry date to 30 days in the future (for example 2009-12-10). Then select "Create a license from a SKU" and download the license file. This license file can then be installed in the License Manager and will expire on the set date.