Possible to get cursor into date lozenge and modify its text

See demonstration in attached video.  

Date Lozenge Bug.mov

Steps

1. Add a date using //, and then a mention with @
2. Use the left arrow to move the cursor through the mention until the first character
3. Press Backspace/delete to delete the first character of the mention
4. Press Backspace/delete again (repeat) and the characters in the date begin to be deleted allowing to type other things in there.

Edit 14/03/2018:

I am struggling to replicate this on 6.8 if I have not previously deleted the lozenge and then undone that delete (using keyboard shortcut or undo button). 

After undoing the delete of the lozenge, the ```contenteditable="false"``` and ```onselectstart="return false;"``` attributes will no longer exist on the datetime object. 

See video:

Date Lozenge Undo Video Trimmed.mov

Steps

1. Add a date using //
2. Delete the date lozenge
3. Press the undo button or use the keyboard shortcut CMD+Z
4. The lozenge can now be typed in and the text within it deleted