Yes, well...I wasn't expecting the thread to get moved over to the M&M forum! What I meant was that I'd searched the M&M forum for anything on this, and hadn't found anything. Not a surprise, really, given that it seems it was Opodo's fault, and could therefore have happened with any airline.

In the end we tried to go standby on the original flight, which turned out to be full, and were put on the later flight. So we did get to Vienna the same day, but hours later, and with some 24 hours of high stress. It appears, from what information we can glean, that Opodo didn't do something (I don't know what exactly) correctly, that the outbound flight was never properly booked, and that they didn't book us onto the later flight until I called them up the day before the flight when trying to find out what was going on. If so, then everything they told us since then was a cover-up job.

Naturally, I'll be looking for due compensation, as this just simply is Not On.

And yes, there are lessons to be learned here. I only ever use TAs when they seem to have better fares than the airlines' sites - frankly, I think I'll go back to booking direct. And I always thought checking my plans over and over was for the crazies who read internet forums on travel...um...oh, that's me. Seriously, I figured I'd booked the flights, what did I need to do until check-in at T-24?! But from now on, I guess I'll have to start checking on things a bit more often...