Created attachment 108224 [details]
Writer: after update vs after reinstallation
There was LibreOffice 4.2.0 or 4.2.4 (sorry, I don't remember, what) on my computer. I have installed 18.104.22.168 and get some strange symbols in my formulae (see attachment, upper half of a picture).
System reboot does not solve it. But removal via "Programs and features" and installation do (see attachment, lower half of the picture).
It's a known issue.
*** This bug has been marked as a duplicate of bug 76239 ***