PPSSPP runs fine on my IGP, not on my HD7970

[mamadoo06]

Hello,

I'm using the last version of PPSSPP on :
1) My desktop PC - Radeon HD7970 Ghz + i5 Quad
2) My laptop - IGP + i5 dual
3) Macbook Pro retina 13 with IGP (iris) + i5 dual

PPSSPP is great and runs perfectly fine with God of War and Wipeout on my machines 2) and 3)... but runs slow on my 1)... which has the most powerful CPU and GPU

Is there a known bug with AMD GPU ?
How to understand and fix the problems ?

The incredible thing is that on my machine 1), if I use the Fast Forward key, it accelerates a lot the games which runs perfecly smoothly during fast forwarding !

Many thanks