Underline not rendered correctly

[zihlmalb]

As the underbrace also underline will not be rendered correctly:

Input:

require 'mathematical'

renderer = Mathematical.new()
result = renderer.render('$Q=\underline{A \cdot B \cdot C}$')
File.open("out.svg", 'w'){|f| f.puts result[:data]}

Output:

Don't know what that funny dotted ellipse does mean.

Comment:

Please fix this. Its affecting asciidoctor-mathematical for ages and should be solved finally. The same thing for the underbrace-issue. Thx.