PO prepayment - sales tax posting account

Hi,

I've posted a Prepayment invoice in a PO. And in the journal for this posting, the sales tax account is not the same as the one defined in the "Pre" posting profile:

Here are the setups:

Could you please tell me what causes the mismatch in Sales tax account in the Posting profile & the voucher? And what should I do in order to correct this issue?

Thanks a lot in advance!

S.