Nonprinting Characters no longer appear
Solution 1:
(Found at http://en.libreofficeforum.org/node/1697 )
Check your settings at:
Tools > Options... > LibreOffice Writer > Formatting Aids "Display of"
Check the box for "Paragraph Ends" or whichever non-printing character you want to view or hide by toggling. If all the boxes are unticked, you'd not see any non-printing character (which may explain why nothing changes when you click the button or use ctrl+F10).