My F18A was still on firmware v1.3 so I updated it to v1.8 but still have the same Antarctic Adventure bug. So, I'm guessing that this might be an F18A specific bug. Would be good to get confirmation, or otherwise, from others with F18A and non-F18A RGB systems.
Sprites are sometimes obscured by taking advantage of the 4-sprites-per-line limitation, which the F18A has disabled by default (IIRC). If it's affecting your gameplay, there's a jumper you can set on the board to default to the classic 4-sprites-per-line behaviour (and F18A-specific software can still override that.)
Edited by Tursi, Sun Aug 12, 2018 3:40 PM.