ADIRU Questions

It's been a few days of playing around with the PMDG T7 now and I have question about the ADIRU I haven't run across an answer for after intelligently searching the manuals (I say this because I have not read the 3,000+ pages yet).

ADIRU after long turn/secure: I don't expect this is a bug, but am wondering if anyone can give the systems logic.  I notice that the PFD maintains the ground/sky with attitude indication after the ADIRU is turned off when securing the aircraft (and remains there after a long turn as such).  It does indicate it has no heading data.  After switching the ADIRU on to align it, this attitude indication is lost until alignment.  I am trying not to treat this like the little Boeing brothers, but am used to the 737NG (PMDG) and 763 (LDS) where attitude data is lost as soon as the IRS (equivalent system) is switched off.  So what's the system logic for when the ADIRU loses it's attitude data?