This only happens with Framework V3 and i have not pressed enter and i end on a Space, well lots of them, i'm not sure why this is as the hacked up mixed version's of V1 and V2 i did to get it working on Linux does not have this problem with the Scroller.
Viewing post in Space Swarm 64 Version 3.2 (C64) comments
I just found that out as i am updated this very game to remove the other bug from the older framework also put some animated chars back ground animation with means i had to change the mapping a bit then started looking at the code for scroller and saw a commit about the @ bit, so just tested and it's working now.