Note: This is not about Less.js handled @import.
@import rules must appear at the beginning of the document before all other rules except @charset. https://www.w3.org/TR/CSS2/cascade.html#at-import
Example: This CSS will cause the browser to render the selectors with the appropriate font.
Example: This CSS will cause the browser to ignore the @import due it being concatenated in the middle of the output.
It looks like ResourceLoaderFileModule is calling out to CSSMin to handle concatenating all of these files together and in the process handling @embed. CSSMin is detecting the @import blocks so it looks like it might be simple to strip those out and move them to the top.