Why are there two different paypal checkout pages?

It's come to my attention that customers can get different Paypal checkout pages. Sometimes it's pretty straight forward, other times not.
I contacted Paypal and received the following response:
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I reviewed your website and refer it to the screenshot you sent us and it appears that your buttons are set up differently. Some buttons was created and integrated using our new 'Express Checkout' button which will show a different page when making a purchase. The first picture is our 'Simplified Express Checkout' while the second picture appears to be our 'Classic Interface'.

I recommend to consult your web developer and ask if he or she can create a button and integrate it using just one interface in order to avoid any confusion. I assure you that this is just depends on what or how your buttons were created and how it was integrated.
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Does this make any sense to you, and how can I get this resolved?

Thanks,
Michael