Missing monospace font rendering in commits after tbb-6.5a1-build1

I'm testing an alpha build on linux built from recent code, and rendering of monospace fonts seems to be broken. It shows up as squares or blank.

It's actually a snowflake build I'm testing, from comment:9:ticket:19001. The exact commit is a83d3993 in the snowflake branch, which is built on top of bd20a2aa in master.

I'll attach a screenshot that shows that page contents and browser chrome (the inspector) are equally effective. Even the text box to create this ticket is broken in textarea mode (text is visible in wysiwyg mode).