CKEditor - Bug in undo

**Describe the bug**
Using Source view the undo action does not work, but in the wsyiwyg editor it does work.

**To Reproduce**
Steps to reproduce the behavior:
1. Using Source View make some changes
2. Try to ctrl-z 
3. Nothing happens
4. Click Source
5. Try to ctrl-z
6. Should undo

**Expected behavior**
Undo should work over either screen
