Why Invoice contains tax for tax exempt customer

[JeanChristophe]

Recently we noticed an issue when generating invoice for tax exempt customers. 
We found that for products tax exempt works correctly, while for other products it does not.

Incorrect (draft) invoice with tax: INV00095228 

Correct (posted) invoice without tax: INV00092035 

Can you please advice how we can solve this issue?

[JeanChristophe · Accepted solution]

•  INV00092035 bill the subscription A-S00007672 for which  the "Customer Name" and "Invoice Owner" are the same and the account is "Tax Exempt".
  
  
• INV00095228 bill the subscription A-S00008154 for which the "Customer Name" and "Invoice Owner" are different : 
     the Subscription Owner is not "tax exempt".
     and the Invoice Owner which is the same as the other Subscription , is "Tax Exempt"

     Both Subscriptions have the same invoice owner which is "Tax Exempt"
     and the A-S00008154's account owner is different and it is not "Tax Exempt"

    On the tenant "Billing Settings" / "Billing Rules" we have :

              "The Rule Calculate taxes using information from Customer Account of:" is set to "Subscription owner"

    The invoice INV00095228 , for A-S00008154, contains the tax because the "Subscription owner"  is Not "Tax Exempt". :