xreader cannot "save current settings as default"

[pepperminty]

I use Mint 18 Sarah MATE 64-bit
xreader version 1.0.8.

How to reproduce problem:

Open any PDF file in xreader. (By default, double-clicking on a PDF will have it open in xreader.)
Reverse the colors, either by typing Ctrl+I, or by going to View/Inverted_Colors.
Save settings, either by typing Ctrl+T, or by going to Edit/Save_Current_Settings_as_Default.
Close xreader.
Open a PDF (it could be any PDF, even the same one).

What happened: PDF opens with non-inverted colors.
What I expected to happen: PDF should open with inverted colors (black background, white text).
Problem happens all the time.

This problem occurs on my MATE, Cinnamon and XFCE computers.