Any chance I could see that bit of the code you're using? Either here or in a quack or something. I don't see a paypal link on your page at all. (Am I being blind again?)
Sometimes if you have the same form action, method, or input type, you can actually trigger one thing with the other (because the html can't differentiate). It may also have depended on where you were trying to put it - if it was next to or under the comment form, you may have pasted one bit of code into another so the browser thought they were all the same form.
We would have to see the paypal code though - you probably removed the button from your page because it wasn't working. :]