Inheritance of top level selector only

[Alexander Sergeyev]

.row {
width: 960px;
margin: 0 auto;
overflow: hidden;
}
.row .row {
margin: 0 -10px;
width: auto;
display: inline-block;
}
header extends .row {}

outputs

header header,
.row .row {
margin: 0 -10px;
width: auto;
display: inline-block;
}
header,
.row {
width: 960px;
margin: 0 auto;
overflow: hidden;
}

expected

.row .row {
margin: 0 -10px;
width: auto;
display: inline-block;
}
.row,.header {
width: 960px;
margin: 0 auto;
overflow: hidden;
}

"Row-row" part is taken from 1kbgrid.com.
So, how could we handle this case?