Webinstaller doenst flash vendor.img on oriole factory images (customrom, not protonaosp)

[koen01]

i generated factory images for oriole for my own custom aosp based rom.
They flash fine with fastboot on linux/mac os / windows.

But if i flash them with the android-webinstall tool the oriole wont boot (sunfish and coral do boot with images flash with the webinstaller)

in google chrome console i see following ragrding the vendor img

for some reason the installer thinks the vendor.img is 4096 bytes? Where does this come from?

flashing the same factory image with fastboot on windows gives this output for this step:

[safarifox]

any one have a solution ?