Brendand,
Do me a favor and run the AP Aging, for the Vendor Ebay, in Detail. Also, go to the Vendor Card and open History/Ledger Entries and take a screen shot of the Invoice and Credit Memo record.
If you applied the CM to the Invoice, nothing should appear. Your images of the $10 activity tile is what you are referring too. If yes, pplease also click the tile and send the screenshot.
I have my test case and can review my example to yours.
Thanks,
Steve