Nested mixin bug for Multi selector

[evmek]

for example

M()
  "[a],[b],[c]"

{M()}  
  &{M()}
    x y

should be generated as

[a][a],
[b][a],
[c][a],
[a][b],
[b][b],
[c][b],
[a][c],
[b][c],
[c][c] {
  x: y;
}

but it is generated as

[a][a],
[b][a],
[c][a],
[a] [b],
[b] [b],
[c] [b],
[a] [c],
[b] [c],
[c] [c] {
  x: y;
}

bug is

The first 3 selector right, others wrong, no spaces between them

[a] [b],
[b] [b],
[c] [b],
[a] [c],
[b] [c],
[c] [c]