With the code listings on this page, it seems like there's something wrong with the CR/Line feeds.
I just did a quick test on a test page here on Itch with code from the ULAplus spec and it shows up normal when creating a code-block.
The only thing that Itch does is remove "empty" lines (ie before the "header:", "basic:" labels, etc.) but that can be easily fixed by putting only a space on those lines.
