I had to do the yesterday. UAL.com would not accept my 20% cert at all for a LAX-ICN-LAX ticket. The cert was clearly good for worldwide travel.

I called web support. The agent put me on hold and told me that my cert was good for every country except for South Korea.

Hmmm.

Her sup then stepped in and got me squared away!

I now am out of pocket $750 for a roundtrip upgrades ticket!