How to unhide transaction entry list in loan account

I established a loan account with my car loan balance, and will be making payments from a checking/bank account. However, when I enter a payment transaction in the bank account, I am unable to select the loan account as a category (which would have the effect of transferring the debit to my bank account as a credit to the loan account). When I view my loan account details, there is a check box "Hide in transaction lists" that is checked and greyed out. I am confused. Why can I not enter a payment transaction in my bank account and have my loan account credited, as I do with credit card accounts?