math preview not working (lyx-2.1.3, fedora-22)

[Neal Becker]

I know it used to work, but something broke.

If I turn on math preview, it does something horrible.  It looks like the 
preview of math now occupies about 1/2 of the screen, making the screen 
quite unreadable.  Like if I wrote $x^2$, there is a box showing a preview 
of this single x^2 that occupies like 1/2 of the screen.