Is this normal?

I was trying to pay for something using bitcoin, and every now and again (more often on the first copy attempt) it would copy a completely different address?

I didn't double check the address upon checkout, and the seller says that address has nothing to do with them.

Clarification: When copy+pasting this address, whether you use the button, or do it manually, sometimes throws out a completely different address that's (according to him) has nothing to do with the seller.