Functional tests need to be run with visual editor enabled (Admin -> Rich text editor).
I could not reproduce this reliably... and I didn't get errors in Edge (although they have been reported).
The most reliable way I could get to reproduce this was open the create issue dialog, switch to text mode. Open again, then switch to visual mode. Open again, on sometimes (but not always) on that occasion the field would be empty.
Also, just repeatedly reopening the form left the field empty sometimes.
It must be a timing issue, we're probably trying to set the value before the control is ready.
In at least one case, the occurrence of this issue is related to which tab the editor appears on