Superscript and subscript behat tests occasionally fail

I am experiencing up to 4 failures with the behat tests for the atto superscript and subscript behat tests. The failures are:

(: failed steps (:

01. "_Submarine" text was not found in the page
In step `Then I should see "<sub>Submarine</sub>"'. # behat_general::assert_page_contains_text()
From scenario `Subscript some text'. # moodle/lib/editor/atto/plugins/subscript/tests/behat/subscript.feature:6
Of feature `Atto subscript button'. # moodle/lib/editor/atto/plugins/subscript/tests/behat/subscript.feature

02. "_Submarine" text was not found in the page
In step `Then I should see "<sub>Submarine</sub>"'. # behat_general::assert_page_contains_text()
From scenario `Subscript some text in enclosed in superscript'. # moodle/lib/editor/atto/plugins/subscript/tests/behat/subscript.feature:23
Of feature `Atto subscript button'. # /home/brianb/Sites/moodletotara/lib/editor/atto/plugins/subscript/tests/behat/subscript.feature

03. "^Helicopter" text was not found in the page
In step `Then I should see "<sup>Helicopter</sup>"'. # behat_general::assert_page_contains_text()
From scenario `Subscript some text'. # moodle/lib/editor/atto/plugins/superscript/tests/behat/superscript.feature:6
Of feature `Atto superscript button'. # moodle/lib/editor/atto/plugins/superscript/tests/behat/superscript.feature

04. "^Helicopter" text was not found in the page
In step `Then I should see "<sup>Helicopter</sup>"'. # behat_general::assert_page_contains_text()
From scenario `Superscript some text that is enclosed in subscript'. # moodle/lib/editor/atto/plugins/superscript/tests/behat/superscript.feature:23
Of feature `Atto superscript button'. # moodle/lib/editor/atto/plugins/superscript/tests/behat/superscript.feature

While the failures were not happening every time, the were failing enough for me to track down the cause - the atto editor not updating the master text area all of the time (although I wasn't able to replicate this outside of behat tests) when running in firefox.

I've replicated it on 2.9, but haven't tried in other versions.