Did you try copying all the 924's .cal files onto your DHO800?
I see no reason at all why the hardware would be different.
I've tried this combinations:
1) 924 vendor.bin on 804 firmware: non correctable DC offset, voltage accuracy is low, fluffy waveform
2) 924 vendor.bin on 804 firmware but with 924 cal files: non correctable DC offset, voltage accuracy is low (1.6%), fluffy waveform
3) 804 vendor.bin but with 924 cal files: no DC offset, voltage accuracy is low (1.6%), waveform is normal (not sure)
4) back to the original unlocked DHO804 vendor.bin and cal files:
no DC offset, voltage accuracy is high (0.26%), waveform is normalBTW, waveform fluffines, probably, would dissapear by itself if I keep the scope with no power for 12H or more.