Why does @extend work but not @include?

Question

css

.header-prev{
@include all-icons-sprites(arrow-left);
position: absolute;
bottom: -35px;
left: 0;
&:hover{
@include all-icons-sprites(arrow-left-h);
}
/* Here's how it works...*/
.header-prev{
@extend .icons-arrow-left;
position: absolute;
bottom: -35px;
left: 0;
&:hover{
@extend .icons-arrow-left-h;
}
}
Koala compiles both code without errors.

Answer 1

Most likely a problem with the mixin. It would be nice to see his source)

Answer 2

In less the same crap