ConPTY and terminal graphics

[Thomas Wolff]

When the cygwin conpty adaptation is activated for the first time, it 
spoils any graphics (e.g. Sixel output) present on the screen. It 
probably replays the output code but somehow modified. Test case:
gnuplot -e "splot [x=-3:3] [y=-2:2] sin(x) * cos(y)"
cmd /c ver

If repeated, it does not happen again. Also graphics that are already in 
the scrollback buffer are not affected.
(Not a big issue.)
Thomas