I'm having some control issues

I have installed a ServoStic, 2 action buttons, 2 player start buttons & 2 Coin. They are connected to the PC with a Kade encoder. For the most part everything seems to be working fine except while playing "vs Super Mario Bros" I get what feels like key blocking which (afaik) shouldn't happen with the Kade.
I will try an explain whats going on.. I am moving (right), holding (fast/fire) and when I go (left) then (right) again mario sometimes becomes stuck until I let go and start over.
When I force the ServoStic into 4-way mode it plays fine.. Everything I find online states it was a 8-way but I don't remember the game playing like this with my old iPac/Happ 8-way panel. I cant figure out if its the stick, the kade or the idiot mashing the buttons
