My sneaky bank cashed my mortgage check 1 week later after mailing it, why?

I have a loan with a bank and usually when I mail them a check, they cash it 3 days later, however a few times I've noticed they wont cash it until a week later. This of course builds interest in the mean time; The longer I wait to send them a check, the more interest I will pay on that payment.

so you think they do it on purpose? Your thoughts

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