convert -size 100x101 xc:white \
-fill none -stroke red -draw "polyline 0,0 25,75 255,255 255,0" -flip 1tmp1.png

But the following (equivalent MVG syntax), which used to work in my scripts, now does not:
convert -size 100x101 xc:white \
-draw "fill none stroke red polyline 0,0 25,75 255,255 255,0" -flip 1tmp2.png

Am I doing something wrong in my syntax or is this a bug?