Attached 2 screenshots. First shows the bug. Second shows the exact same
command ran again, in seemingly identical circumstances, but without the
hyphens infesting the document this time.

(Note especially the "2/258-" in the corner of the second screenshot;
the hypens even got into a UI element!)

Document is from http://www.gutenberg.org/ebooks/20869.epub.images

I have been seeing this bug in a lot of books I open in fbreader over
the past 6 months or so.

Window manager is xmonad, and I kind of get the feeling it may have to
do with the window being constrained to a smallish tile as shown here.
However, I've also had the hypens come when the tile was the full width
of the screen.

Dear Maintainer,

in my case, the bug is caused by pango's auto-hyphenation feature (which
was adeed and enabled by default, causing a lot of similar breakage in
other software), but the underlying cause is using uninitialised memory,
which is why it is happening randomly.

I fixed this by initialising the PangoAnalysis struct in
zlibrary/ui/src/gtk/view/ZLGtkPaintContext.cpp, in the constrcutor
(ZLGtkPaintContext::ZLGtkPaintContext), by adding:

  myAnalysis = PangoAnalysis ({0});

This might be a problem elsewhere in the code, which I haven't
investigated, as with this fix, fbreader becomes usable again.