seems like an odd glitch to just randomly happen. principal-no-date is a payment type that is set when the transaction is conducted. when done online, it's batched and processed automatically, but it's not really possible for the system to change it by itself. and it should never touch human hands again, once you click submit. that's like saying your voting machine changed your vote from hillary to trump on its own. and we know that could never happen.
find a better bank. if their system is randomly changing transaction type from a glitch, then it can also randomly change dollar amount or account number. there should be bells ringing in their processing department if this happens more than zero times. and for them to act like it's just some weird quirk and not get worried about it, tells me they don't really give a shit about a lot of important stuff. don't let them anywhere near your money.