Message in release date edit form

As another user noted here, if you click to edit release dates on a series page in the new overlay edit feature, this message appears:

Release dates cannot be added for titles that are in-development or in-production

It appears even on old series.

The reason it is not possible to add a release date on a series page is different. It was disabled because you want them added to episodes. 

I don't see why there would be a rule against adding release dates to in-production titles.