How is the Tax Event Class Code automatically added to Transactions?

In the tax rules you can base your rules on Tax Events, where one of the Tax Event Class Codes is INTERCOMPANY TRANSACTIONS.

I expect the PA Internal Invoices and the AGIS Intercompany invoices to be assigned this Tax Event Class Code.

However when I look into ZX_LINES the tax event class codes assigned to the transactionswhich I consider as INTERCO, they have SALES TRANSACTIOn and PURCHASE TRANSACTION.

Is this a bug and do I need a patch?

Is there a setup step missing?

Is there another table than ZX LINES where the correct tax event class codes are assigned?