In ask.libreoffice you'll find many (many!) threads in which users ask why they are not able to delete content anymore, or pointing out that new text is in a different color, etc. All those "problems" come from accidentally enabling the "track changes" feature.
In all keyboards, Shift and Ctrl keys are close together, and that means that's quite easy to, by accident, hit Ctrl-Shift-C (the default shortcut for "track changes") instead of plain, and quite common, Ctrl-C or Shift-C. This is specially true for compact keyboards such as those you find in laptops / notebooks.
My suggestion is therefore to consider a change in the default shortcut for "Track Changes" so it's more difficult to activate that feature by chance. Perhaps a four key shortcut (it's almost impossible to hit Ctrl-Alt-Shift-C by accident) will save a lot of people, specially new users, from a sudden puzzling situation.
 Just one of the latest threads as example:
but seriously, this "problem" appears so often that it deserves consideration.
And it's easy to confuse with ctrl+alt+F10 (insert comment). I suggest to not have a shortcut for this very infrequently activated function.
(In reply to Heiko Tietze from comment #1)
> And it's easy to confuse with ctrl+alt+F10 (insert comment). I suggest to
> not have a shortcut for this very infrequently activated function.
So let's do it and remove the shortcut.
remove <node oor:name="C_SHIFT_MOD1" oor:op="replace"> around .uno:TrackChanges (2x)
*** This bug has been marked as a duplicate of bug 130847 ***