When importing a document for the first time, you will be asked to specify the accounts to be debited and credited in the import confirmation dialog.
When you specify an account, the account you specified is stored in memory with the description payee information used as a unique signature.
The next time you run an import, Prudent will try and find transactions with the same signature and show the accounts to be debited and credited that it remembers.
This memory of the accounts that you'd specified takes precedence over accounts suggested by import add-ons.
You can always change the account assignment that is stored in memory by simply specifying the desired account that you want to assign to again. Prudent will then remember the new account that you assign to for that specific transaction.