git gui: Error when opening dialogs

I have 3 monitors configuration and recently I have noticed issue in ‘git gui’. When I tried to revert changes or merge branch, this dialog appeared:

smalldialog

That caused hang of window. In command line was visible an error:

jarek@lp-jarek:~/Navigo3/master/np$ git gui
bgerror failed to handle background error.
Original error: bad pad value "3m": must be positive screen distance
Error in bgerror: bad pad value "3m": must be positive screen distance

After some googling I have found an issue (bogus DPI):

jarek@lp-jarek:~$ xdpyinfo | grep -A1 dimen
 dimensions: 5408x1152 pixels (0x0 millimeters)
 resolution: -2147483648x-2147483648 dots per inch

And fixed it via:

jarek@lp-jarek:~$ xrandr --dpi 96
jarek@lp-jarek:~$ xdpyinfo | grep -A1 dimen
dimensions: 5408x1152 pixels (1430x304 millimeters)
resolution: 96x96 dots per inch
Tags:  GIT  Ubuntu