I tried also in my 2 devices (Acer s120 gingerbread and LG L9 ics) and it's a bug, I think nobody found it because we are all using buffered rendering on. 
With this strange bug it's noticeably faster also for me (adreno 205 and sgx540 overclocked) but the screen is flickering a lot.
Speed is better because the emulator is rendering graphics at 1/4 resolution, if it's faster that means also your device with adreno 220 is gpu limited at psp's native resolution (480x272).
With this strange bug it's noticeably faster also for me (adreno 205 and sgx540 overclocked) but the screen is flickering a lot.
Speed is better because the emulator is rendering graphics at 1/4 resolution, if it's faster that means also your device with adreno 220 is gpu limited at psp's native resolution (480x272).