Comment 28 for bug 1422626

If it helps, I've put the following code in my .bashrc

if [ "$DISPLAY" ]; then
 activ_win_id=`xprop -root _NET_ACTIVE_WINDOW`
 activ_win_id=$(echo $activ_win_id | awk '{ activ_win_id=substr($0,41,9); print activ_win_id; }' )
 xprop -id $activ_win_id -remove WM_NORMAL_HINTS
fi

I think this removes the WM_NORMAL_HINTS from any terminal emulator. Xfwm then manages to tile the terminal window without gaps, and the tiles are filled correctly.