so from my understanding when I use the spoilers and reversers the spoilers are not supposed to retract until 40 kts. but here in the video you see the spoilers are being retracted when I stop using the thrust reversers. this has been also happening in the Boeing 757, A330, and 777-200ER.
here is the link
Disclaimer:the flying that you see was done on the casual server
Try using the new auto-brakes feature, the spoilers will remain up after 40kts until you turn them off or increase your thrust instead. It also makes it more realistic.