Odd less @import error when *not* using colons after @ımport statement

test.less

body {
	// surprisingly this will not throw an error, but it won't import the file neither
	.mx({ @import: "test2.less"; });
}

body {
	// this will throw an error:
	// SyntaxError: Cannot read property 'rules' of undefined in /Users/johannes/test/less-bug/test.less on line 7, column 3:
	// 6 body {
	// 7   .mx({ @import "test2.less"; });
	// 8 }
	.mx({ @import "test2.less"; });
}

.mx(@declarations) {
    @declarations();
}

test2.less

border: 1px solid red;