I had the same thing for a KL trip this past weekend. Both the outbound and the inbound. I moved seats after the curtain was moved forward, but the app/website continued to show me in my original seat even as the new seat chosen was showed as greyed out for some other passenger.

However, being aware of the bug, I was pretty satisfied that that meant I was actually moved to the new seat - and when time came to check-in, voila, I was indeed in the new seat.