In the Major Incident Workbench's Communication section, when switching between tabs, content added during composing email is not saved.
Activate the Incident Management - Major Incident Management plugin if it is not active already.
Navigate to Incident > Major Incidents > Overview and open any created incident.
If no major incident exists, create one.
In the record, click View workbench.
In the Communication section, click Compose email and write any text in any field including the HTML field.
Without saving the input, switch to the Activity tab and then back again to the Information tab.
Note that the content you added is missing and the form seems to have been reloaded.
This is expected behavior. On switching the tabs in the email client template, the page reloads. Because the context changes, the changes made by the user are not saved.