Post Office Issues: Paying for Postage via eBay

[Buythatcard]

I have been creating postage labels via ebay for quite some time. Never had a problem until today. I mail out over 100 items a week and for some reason one package was returned to me.

This package contained 1 card and was in a bubble envelope.

When I created a postage label via eBay for this item, I chose the following:

First Class Package/Thick Envelope
Package weighed 1 ounce.
Package was about 1/4 inch thick.

Cost was $1.22 for the S/H + .19 for delivery confirmation(You must take delivery confirmation.)
So, total cost was $1.41.

Post Office returned it stating that to use Delivery Confirmation, the envelope must be atleast 3/4 thick and it must be first class parcel. I was told that I need to send it Priority mail which will be an additional $3.49. I complained to the PO and they said that sometimes it gets through and sometimes it gets stopped. If you want to use delivery confirmation, you need to send it Priority mail.
I told them that was absurd. I said that I am forced to take delivery confirmation when I create the postage labels online. Their response was well thats the way it is.

Has anyone else experienced such nonsense and if so what did you do?