I have no idea what's going - it looks like BA is moving Madrid back to T5 on Sunday, and Iberia was in the systems for 1 June (after being pushed back from, I believe, this Sunday, then May).

However, yesterday, all IB flights from this Sunday started showing as T5 again, but they're back to showing T3 now. I thought it might've been a fluke, but heathrow.com also showed IB as T5 from Sunday. That also now shows T3.

Not sure if it was a fluke yesterday, but a pretty major one...