SD/OD question: Actual Ship Date

Hi all, using 9.2. 

When an OD is received, the Actual Ship Date ADDJ on the related SD is being populated with the Receipt Date, which I think is also ADDJ in the F4311.

I'm trying to confirm that is standard (as opposed to a customization) but cannot find it in the documentation.  It's working for our process but seems counter-intuitive that an SD would have an Actual Ship Date because we didn't ship it.  I'd just like to confirm please if you could point me to a document?

Thanks as always for the help,

margie