Originally Posted by
wanderingswede
...As an example - last week I was flying LHR-MAD-LHR in a 24 hour period and checked into both flights and printed boarding passes at the same time. I then changed the outbound at the last minute due to a meeting running over (TA offloaded me and re-checked in) and the inbound flight started appearing as not checked in on MMB without letting me change it. Got to the airport in Madrid and went up to the BA check in with my boarding pass and asked if it was still valid - they said yes so I went through to the lounge and then gate. As I went to board I was red flagged and not allowed to board - turns out that I was never checked in and the check in desk lied to me/didn't bother to check properly...
This happened to you because you were a sameday return. So, it was one check in transaction for both flights. (same for a connection.) When it's one check in transaction for more than one flight, when you're offloaded from the first flight you're automatically offloaded from any subsequent flights. After all, if you're not on the first flight the system will (usually correctly) assume you won't be on the second flight.
Your T/A didn't check you in for both your flights. Why? Who knows.
As for MAD: Yes, the agent certainly missed the fact that you were offloaded. My guess is that they looked at your boarding pass, (14A let's say) and the screen saind you're in 14A so the agent thought all was well. What the agent failed to see was that there was no * or <chng> symbol next to the seat number to indicate that you were checked in. (also there's a comment that would've said, "OFFLOADED BY..." at the bottom of the record.)