MathML is never spoken correctly when encountered using the tab key

Summary

1. Go to http://superkeen.com/web/mathmltest/mathmlfocus.html
2. Tab through the page.

Expected result

MathML mixed with plain text should be spoken correctly many times as:

The fraction two thirds and the exponent two cubed are not equal.

Actual result

MathML is spoken incorrectly as:

The fraction and the exponent are not equal.

or truncated further to:

The fraction

Example

The link provided above provides multiple examples. It's a standalone HTML file without any CSS or Javascript, so it should be easy enough to View Source or to download it.

Additional Information

I am trying to write a math game that students can play entirely with the tab key, but for it to work with Orca, this issue would need to be resolved. As it is now, it seems that there is virtually no way for Orca to speak MathML without using Orca shortcuts to read from the virtual buffer. It would be ideal for content within the "math" element to be routed through the appropriate speech rule engine regardless of its context.

I have filed a very similar bug report to JAWS: https://github.com/FreedomScientific/VFO-standards-support/issues/148

Orca version and build number

Orca on Gnome 3.26.0

Operating System and version

Ubuntu 18.10 (osboxes.org image)

Browser and version:

Firefox 63.0 (64-bit)