As a native Norwegian speaker, I had to look it up to see whether a space was expected or not, as it seems entirely illogical for me to have a space there as they're so closely connected.

The distinction between "fully merged" compounds, hyphenated ones, and ones with spaces is yet another one of those endlessly annoying quirks of English.

> The distinction between "fully merged" compounds, hyphenated ones, and ones with spaces is yet another one of those endlessly annoying quirks of English

Being cognizant of these really helps develop empathy with ESL learners.