Your Dad isn't the only one. I continue to experience some very odd behaviour towards me even though I am only inactive, and not formally disassociated or disfellowshipped.
I used to regularly play sports every Sunday with members of my congregation. They no longer invite me.
I also wasn't invited to an important celebration that was held for a close family member, even though I had travelled a considerable distance to be with him at that special time. My presence at the party would evidently have stumbled some.
I continue to experience "e-shunning" whereby close friends no longer email (or refuse to reply to my emails) now that they know I'm inactive.
I've also noticed that my inactivity seems to prompt elders to bend (or ignore) the rules when it comes to how they should treat me as a brother. It now seems to be perfectly scriptural to (1) gossip about me with others, or (2) phone close family members, or pull them to one side at the meeting, to ask them questions about my spirituality - without approaching or contacting me directly with these questions. Everything is now very "cloak and dagger", which I absolutely can't stand and creates untold stress for both me and Mrs Cedars.
I feel for your Dad, not least because I am very much in the same boat. I am now only a "brother" in name, and not in practice.
Cedars