The only way to know for sure what the issue could be is if everyone reports all the details about their system (modded and what mods and by whom or unmodded) and if they exerience the corrupted graphics or not and when.
Occassionally I have experienced the issue on my Yurkie modded CV that has his Video Mod Board, Pause Button, Power Light Mod, Bios Skip Mod, Power Supply Mod and numerous sockets added for quick chip replacement. We would also have to know for sure if there was any differences in the first run SGM that could cause the issue. Aside from that, possibly a change in the Cartridge PCB was made or a different manufacturer used.
Probably a programming bug, but everything would have to be considered.
Edited by NIAD, Tue Nov 18, 2014 8:12 AM.