Underbrace not rendered correctly

[zihlmalb]

Underbraces are not rendered correctly.

Input

require 'mathematical'

output = Mathematical.new(:format => :svg).render('$\underbrace{\overline{C}\cdot B \cdot A}_X$')
File.write('./underbrace.svg', output[:data], mode: 'w')

Output

What I expect

** Version **
mathematical-1.6.14