Richard Weston,
Sorry that you are seeing this issue with MyEclipse. I could not replicate the issue at my end.
Can you answer some more questions for me to understand the issue better ?
1) Can you share your Build Id from Help > About MyEclipse Enterprise Workbench > Build Id ? Paste the Build Id here for me.
2) How did you install MyEclipse 9.1 ? Is it through Pulse/All-In-Installer/Archived Update site?
3) Can you switch to a new workspace, create a new HTML, select the Doctype ‘HTML 5’ in the wizard and check if the issue persists ? If yes then check the .log file which is located at <workspace dir>/.metadata/.log for any errors of interest. Paste the errors here for me.
Let me know how this works for you.