I had the same issue. Since PayPal has it's preferred order of which accounts will be used first, the only way I could get it to use my Preferred Credit Card (or Debit Card) was to REMOVE my Checking Account from my account. Then, I set the Card I wanted as my default payment source, and now it will always use that Card. The only problem here is that if you remove your Checking Account, then you apparently have limits on how much can be paid via PayPal. I don't know what those limits are, but they have not impacted my purchasing.
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