Strange bug with myGLCD.drawBitmap when called 6 times

Hello everybody,
I buy a display with a capacitive touchscreen, i try to use myGLCD.drawBitmap, using PROGMEM and load my image on Flash, without SD/card.

I look my image on display, i want to change the screeen background (with another image) when I press with a touch on the screen.

For example like principal menu and under menu.

Have you some ideas?
Thanks
Francesco Noto