MS Graph API + Shared Calendar bug

Hello, 

Recently encounter an issue like below, it seems to be a bug:

I have 2 accounts A and B(they are in the same tenant).   A shares a calendar with B

Then  i  login  the Graph explorer with  account B,  and i invoke :  https://graph.microsoft.com/v1.0/users/{account A}/calendar

the result is : 

However whether i assign "View private items" permission,   "canViewPrivateItems" won't reflect the real state.  What's wrong?

can anyone have idea ?

Thanks