Not sure why this is happening. Scroll around the script with your mouse, and control it with the S and space bar keys. It uses hacked blocks, so I doubt the Scratch team is going to be fixing this bug - maybe we can get some part of the community to fix it and make a pull request to LLK/scratch-flash? ;) Turns out if you set a variable to the value of the arg, the bug doesn't occur. Apparently it's limited to just the direct block arg.. weird..
