The system is HP Envy 700-215xt, ROM Family 2AF7, latest BIOS 80.16 Rev. A installed, also latest Intel video driver (though intel video driver has no part in the problem). The graphics is integrated Intel HD4600 in i7-4770 CPU, video out through DVI port on the mainboard.
The problem appears when connected to an ultrawide display with UW-UXGA resolution 2560x1080, model is LG 29MA73V.
On boot-up (from cold or a reboot all the same), when the HP logo is shown, the bottom part of the screen is filled with garbage, various color dots. The resolution at this point is 2560x1080 and is detected correctly, checked by monitor info, and also as the HP logo is round and not strethed as it would be at 1920x1080 resolution.
The number of colored lines appears to be 270, which coincides with (2560*1080-1920*1080)/2560. My understanding of the cause of this is that when drawing this splash screen BIOS fills with black only the area of 1920*1080=2073600 pixels, but since the resolution is detected correctly, to the screen goes 2560*1080=2764800 pixels, hence (2764800-2073600)/2560=270 lines of garbage.
I think this needs a BIOS fix, which would be quite easy to do.
