[BUG] syntax highlight for nested arithmetic expressions is wrong

[Coelacanthus]

install f-s-h, and type this code in zsh:

echo $((((((1))+2))+3-$((6)))) 

it will look like this:

But the two parentheses around the right side 6 should use the same color, because they, like the two outermost parentheses, represent the overall arithmetic syntax.