Does invalidate the strategy of using IE 10 compatibility to work around this issue?

I will put in release notes for Sakai 10.6 that if you have to use IE with this option you might consider making it IE 10 compatible , but please QA test it before you deploy. Here is the property -
sakai.X-UA-Compatible=IE=EmulateIE10

Test plan for 10.6 on on https://trunk-mysql.nightly.sakaiproject.org/portal/

1. In IE 11, create a course site with a dummy roster and add the Lessons tool to it

2. Add an instructor and student account to the site

3. Become the instructor and navigate to the site

4. In Lessons, click the A button or Add Content > Add Text to open the editor

5. On the editor toolbar, click the Record Audio Clip icon (note: You may need to allow/upgrade Flash)

6. Click the Start Recording button and say (or sing) something

7. Click the Stop Recording button. You can Preview or just Post Recording. The recorder will encode and eventually post the recording in a player in the editor.

8. Save the new text/content.

9. As Instructor or Student in IE 11, you should see an audio player that you can play. The error that should be fixed is the Invalid Source that appears in IE 11.

Is there a Test Plan for this then? Do we want to push to get this into 10.6 ?

I'm not sure I'm clear on what needs to be tested or how to test it.

I think these issues you're talking about are more problems with which are not something anyone has put in a fix yet for. It involves implementing and testing some IE11 specific hack. Basically if you need IE 11 support the easiest is to just set the sakai property to put compatibility mode to IE10 which should work fine.

1. The default for Sakai 10 is IE 11 but this won't work for audio recorder.
   sakai.X-UA-Compatible=IE=EmulateIE10

Once the majority of people upgrade to Windows 10, Edge doesn't have any problems with the flash tag and we can remove it ()