Fresh installed Ubuntu 16.04 included Libre office 5. In the dialogue windows however many (not all) headings in bold character display as black variable squares, unreadable, making the use of it difficult or rather impossible. Using the check-/text-/or scroll-box under the heading can/may change a readable heading to unreadable. For me, this is serious and makes the use of Libre office rather impossible.
Created attachment 126674 [details] Screenshot of dialogue in calc
*** Bug 101391 has been marked as a duplicate of this bug. ***
Update at least to 5.1.5, or better, to 5.2. This was already addressed. *** This bug has been marked as a duplicate of bug 99446 ***