unexpected result with Nearest upscaling in ffmpeg

[VD-NVencC]

while going through a list of up-scaling options for ffmpeg I noticed libplacebo nearest wasn't the same output as scale and zscale
is there another step I'm not accounting for?

ff611 -hide_banner -i 4.png -vf scale=-1:4096*2:neighbor -vcodec bmp -f framemd5 - -nostats | findstr 0,
ff710 -hide_banner -i 4.png -vf scale=-1:4096*2:neighbor -vcodec bmp -f framemd5 - -nostats | findstr 0,
0,          0,          0,        1, 268435510, d524ad2f60c32b3201a444a0bc2bc8db

ff611 -hide_banner -i 4.png -vf zscale=w=4096*2:h=4096*2:filter=point -vcodec bmp -f framemd5 - -nostats | findstr 0,
ff710 -hide_banner -i 4.png -vf zscale=w=4096*2:h=4096*2:filter=point -vcodec bmp -f framemd5 - -nostats | findstr 0,
0,          0,          0,        1, 268435510, d524ad2f60c32b3201a444a0bc2bc8db

ff611 -hwaccel vulkan -hide_banner -i 4.png -vf libplacebo=w=4096*2:h=4096*2:upscaler=nearest -vcodec bmp -f framemd5 - -nostats | findstr 0,
ff710 -hwaccel vulkan -hide_banner -i 4.png -vf libplacebo=w=4096*2:h=4096*2:upscaler=nearest -vcodec bmp -f framemd5 - -nostats | findstr 0,
0,          0,          0,        1, 268435510, e0b1e7da015e2c4b59cb43d654e6a4a6

the difference as counted by Pixel Color Counter was 5,898,700

source used below

[VD-NVencC]

ff611 -hwaccel vulkan -hide_banner -i 4.png -vf libplacebo=w=4096*2:h=4096*2:upscaler=nearest:dithering=none -vcodec bmp -f framemd5 - -nostats | findstr 0,
0,          0,          0,        1, 268435510, d524ad2f60c32b3201a444a0bc2bc8db

I recently tried to playback a .png in mpv (v39) and it couldn't display it losslessly without adding dither-depth=no to my config with dither=off already, and that exercise helped me track this down.