It may be a problem with how the plug-in interacts with the page. However, it still involves whatever is happening on the admin panel. If it was as simple as saying "It's the Plug-in", then the plug-in would be having problems with other sites and pages as well. But it isn't, that I've seen. Something on that page is causing issues that the plug-in can't handle.
Now, if the WordPress people decide that they don't care about how Paypal interacts with blogs, that's their choice. They can ignore the issue, and hope that Paypal fixes it themselves. However, Paypal is not a small company. A lot of people use their services, especially in the blogosphere. I think they at least owe it to people to look into the issue.
Either way, it's a bug, and I've reported it. It's up to them to decide whether or not they care. I recall several bug fixes where WordPress doesn't display correctly in IE. That's an IE problem, not a WordPress problem. However, sometimes you have to make sure that those issues that effect your customers are fixed by you, even if it's not your fault.