Kit & Component Sales Order lines

Hi everybody,

i would like to understand the logic with wich sales order component lines of a Kit (K) are closed and reopen when i change the header request date. I create a sales order with P4210. One K line generate all the related components lines. All the components are standard with lnty='S'

After this i change the header DRQJ, system show Kit selection P41351 and after OK button on P4210 some of theese componet are closed (980/999) and reopened. Lines are equals.  I don't understand why and only for some components.

Thank you