When using TinyMCE and using insert | code sample, the TAB key to insert TAB in the code does not work. Instead, the focus is lost and moved to the "Cancel" button.

Steps to replicate:
1. Go to the course page
2. Under any section, click “Add an activity or resource”, then click “Page”
3. Fill in these fields:
Name: (anything of your choosing), e.g “hello”
4. In “Page content”:
Click Insert → Code sample
Click on the dropdown menu under language , then “Python”
5. for first line type in “def foo():”
6. insert a new line by pressing enter
7. Since we want an indent, we press tab

RESULT: The focus is lost and no tab is inserted. The focus is shifted to the "Cancel" button