Nested Selectors Break Minification

I've noticed that nested selectors are interfering with Lightning CSS's minification process
Minification works correctly for non-nested selectors, but it fails to combine rules when nesting is involved:

Non-nested (works correctly):

.bar.foo {
    color: red;
}
.bar.foo {
    color: green;
}

This correctly minifies to: .bar.foo{color:green}

Nested (doesn't minify as expected):

Playground

.bar { .foo { color: red; } }
.bar { .foo { color: green; } }

This produces: .bar .foo{color:red}.bar .foo{color:green}

Nested with nesting feature disabled:

Playground

.bar { .foo { color: red; } }
.bar { .foo { color: green; } }

This produces: .bar{& .foo{color:red}}.bar{& .foo{color:green}}

Expected Behavior

The nested selectors should be minified and combined similarly to the non-nested version, resulting in:
.bar .foo{color:green}

Actual Behavior

The nested selectors are not being combined, resulting in duplicate rules that could be further optimized

Start with the linked Lightning CSS playground and compare the non-nested, nested, and nesting-disabled examples. Trace the minification path for nested selectors and add coverage for the reported input; done means the nested rules combine to produce .bar .foo{color:green} without changing behavior.