If you change the size of an object using any size related blocks in the first block of a when game starts rule, the width and height do not change by the next frame, except on the first play.
It is easiest to see with code like this:
I use this bug for most of the restart detectors in this project:
This does not affect browsers.
It could be that the second frame is being started before the width and height is set on restarts, but the extra delay between the two on the first play gives it enough time.