I think you'll find this may have something more to do with Taipei airport.

Around a month ago I transited on seperate tickets from Eva to Cathay. Upon arrival I proceeded to the transfer desk and asked the Cathay staff for a boarding pass. I already had a mobile boarding pass but thought that they'd need to see my return ticket to the country I was traveling to. Instead he was much more interested in the flight I'd just arrived on and noted down the flight number.