They claimed the firmware fixed button issues because they DID fix it.
I've played on hundreds of games on emulators (N64, Genesis, SNES, PSX, NES, GBA, Lynx, GBC, MAME, AMIGA, MS, GG) , and also many android games (the latest being Carmageddon which works perfect with the mapping tool). I've never had any problems with it.
I suspect you may have both the mapping tool and the hardware mapping on at the same time. This can cause issues because it's literally using two separate controllers with conflicting button inputs for the one game. I use Mupen. What you should do is:
1. open Mupen
2. stop the mapping tool (button emulation)
3. go to Mupen's input options and map the controls like you would with a regular PC or bluetooth joypad
4. Enjoy
To be honest, the joypad on the Archos GamePad works better that my bluetooth controller for Android or my PC controller. With the bluetooth controller, Mupen doesn't recognize the D-pad and analogue controls as separate buttons. With GampePad's built in controls it does.
There is plenty of valid criticism remaining for the GamePad, but it's firmware fix is not one of them.