I seem to have problems in this pre deleting marquee selected item envelope points with the Del key.
Licecap is a bit difficult because it doesn't indicate the Del key press, but here it is anyway:
https://i.imgur.com/otXxi1y.gif
I marquee select points, hit the Del key and nothing happens. Only when I click on a point first the Del key works.
I just briefly checked against 4.731 and it seems to work fine there.