Less, reference not working

问题

My understanding of reference is that it should only include the bits of the imported file it needs. Here it seems to be bringing in other parts?

Main file

.FadedGrid
{
    @import (reference)  './kendo.less';

    .k-grid-header th
    {
        background-color: @input-background-color;
    }
}

kendo.less file

@input-background-color: #000;

/* Nothing from here is used*/
@import "theme.less";

theme.less file

.UnrelatedRule
{
    background-color: #000;
}

output

.FadedGrid .UnrelatedRule {
  background-color: #000;
}
.FadedGrid .k-grid-header th {
  background-color: #000000;
}

Why is UnrelatedRule in there? NB It doesn't make a difference if I change it to

@import (reference) "theme.less";

来源：https://stackoverflow.com/questions/29429159/less-reference-not-working