Hello, I think it's not the same issue. It will be a mapping issue with your controller.
You have to found configuration file of your controller for reicast :
Go here :
/opt/retropie/configs/dreamcast
and open : emu.cfg
Look : [input] part
evdev_mapping_1 = [NAME of your file controller config]
It will be on /opt/retropie/configs/dreamcast/mappings/[your file]
and check mapping.
Good luck.