I don't think it's a bug because if i change the Webstorage action back to how it was before it works the way it should do, the highscore updates when the score is beaten and stays that way until it's beaten again.
Heres how the web action was before -
Webstorage - Set local key "Highscore" to round(CurrentDistance)
It's only when i change it to how it is in the picture above that the problem arises. So i think its a problem with how i've done it, but i'm not sure what i've done wrong. Do i have to do something different with the expression because i'm using Webstorage?