Get this error when building system from an iso created using mksusecd (from SLES12 SP5 install files) and put on a USB Stick:

To use selected repository a matching boot image is needed. Download repository, yes/no.

When I select yes, files are downloaded (from the install files on my USB stick, I suspect) and the installation continues.
Is there a way to avoid this - a switch to use with the mksusecd command (instsys or defaultrepo)? Anybody have an example?

I am creating my own iso because I add folders containing autoyast install files.

I have another way to do this that involves xorriso along with the first 512 bytes from the original iso but it seems like mksusecd would be better.