That helped. Looks like a bug that's specific to CDATA sections. With the "Max line length" set to 0, it shouldn't be adding those line breaks in any case. It doesn't look like anything I can hotfix.
I suspect I may have accidentally run v19 when trying to reproduce it before, because I can't help but reproduce it, or another bad behavior when changing the settings now.
This bug does not seem be In v19, probably because XML beautifier was heavily re-worked. The default configuration leaves the XML the way you want it, without having to even add specific configuration for AllowableValue. (The example file doesn't seem to have the Description tag, so I can't say whether it would need extra configuration or not).