Underline style is not rendered in org-mode markup

Summary

When viewing org-mode files, the underline style (written _with underscores_) is not rendered properly, however its wrapping <span> element persists.

Steps to reproduce

See an example file.

What is the current bug behavior?

It seems that org-ruby gem is used to render org-mode files to html. When testing in isolation, org-ruby produces the following output:

$ bundler exec org-ruby /dev/stdin <<<"The following should be _underlined_"
<p>The following should be <span style="text-decoration:underline;">underlined</span></p>

With GitLab, however, the inline style attribute doesn't appear, leaving only the wrapping <span> intact.

What is the expected correct behavior?

The underline style should be rendered in some way, although inline styles are not very DRY indeed. If avoiding inline styles is desired, org-ruby seems to offer a way to specify a different representation of the underline style, for instance a span element with a certain class.

Output of checks

This bug happens on GitLab.com