When editing source in basic content element (see screenshot) if you try to add a line break by hitting 'enter' key, it doesn't give the new line but automatically saves it. Before it was ok to use and didn't save just after hitting 'save changes'.

Do we know why? Can we fix this? 

Steps to reproduce

• Make available Source option in CKEditor for text and image mtk component (for example by configuring configJsFile=/.resources/ckeditor/config-default.js
• Go to Pages, add a new page with the Basic mtk template. Create a new Text and Image component
• Add some text, click on Source and try to add a line break by hitting 'enter' key

Current result

Dialog is saved and closed.

Expected result

A line break is added to the Rich text field content.

Workaround

N/A

Dev notes

Used to work in 5.7. Not working in any of the 6.2 versions.