Created attachment 643583 [details]
Xorg.0.log

I set my external monitor (VGA1) to be above my docked laptop (LVDS1) and could not drag windows to it (right, left, and below work fine).  If I set VGA1 to be primary I can drag the windows as expected:

$ xrandr --output LVDS1 --below VGA1 --noprimary
$ xrandr --output VGA1 --above LVDS1 --primary

xrandr output, in case it's of use:

$ xrandr
Screen 0: minimum 320 x 200, current 1920 x 2280, maximum 8192 x 8192
LVDS1 connected 1920x1080+0+1200 (normal left inverted right x axis y axis) 344mm x 193mm
   1920x1080      60.0*+   50.0  
   1400x1050      60.0  
   1280x1024      60.0  
   1280x960       60.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
VGA1 connected 1600x1200+0+0 (normal left inverted right x axis y axis) 408mm x 306mm
   1600x1200      60.0*+
   1400x1050      74.9     60.0  
   1600x900       60.0  
   1280x1024      85.0     75.0     60.0  
   1440x900       84.8     75.0     59.9  
   1280x960       85.0     75.0     60.0  
   1366x768       60.0  
   1360x768       60.0  
   1280x800       84.9     74.9     59.8  
   1152x864       75.0  
   1280x768       84.8     74.9     59.9  
   1024x768       85.0     75.1     70.1     60.0  
   1024x576       60.0  
   832x624        74.6  
   800x600        85.1     72.2     75.0     60.3     56.2  
   848x480        60.0  
   640x480        85.0     72.8     75.0     66.7     60.0  
   720x400        85.0     70.1  
   640x400        85.1  
   640x350        85.1  
HDMI1 disconnected (normal left inverted right x axis y axis)
DP1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
HDMI3 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
DP3 disconnected (normal left inverted right x axis y axis)

I also see these in .xsession-errors, but not sure if it's related:

Window manager warning: Region to merge was empty!  Either you have a some pathological STRUT list or there's a bug somewhere!

Also attached Xorg.0.log in case it's helpful.