Well, it's certainly a round-trip; the use of two carriers doesn't change that.
It's not two one-way fares, since it is stated that there is a thru fare. The combinability rule for the fare, which I think is usually fare rule #26, would have to read "DIFF-DIFF-DIFF" for both fares.
[This message has been edited by RichG (edited 01-07-2001).]