This occurs with both PS2 Save Builder and mcIconSysGen as detailed:
The correct shift-JIS spacing character for PS2 saves is 0x8140 (as used by real games), not 0x823F (used by mcIconSysGen) or 0x8100 (used by ps2save-builder).
(source: dlanor at www.ps2-scene.org forums)
After editing/creating an icon.sys file open it up in a hex editor and alter the shift-JIS as needed before saving and adding/updating to a save.
Posted in: Specific save related information