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When you reverse a transaction in the accounting folio, you could be reversing a transaction that was generated automatically - by the business model - or added manually.
If you reverse an automatic transaction and then reprocess the reservation after that, the business model will regenerate the transaction, and you will see it in the accounting folio as an unreversed transaction (the 
will not be grayed out anymore).
This does not happen with manual transactions. They stay reversed even if you reprocess the reservation.