Simple test:
Have a skins/X/resources/scss/page.scss file which contains:

@import "skin://resources/scss/test";

Have a skins/X/resources/scss/_test.scss file which contains:

body {
	background-color: red !important;
}

In DEV mode, change the background-color in _test.scss file and refresh your page => update is not take into account
We need to edit page.scss to see the modification

Very very annoying for skin declination that edits only the SCSS imported to 1, 2, 3 or more levels.

Clearing all caches as no effet