This an approximately 21’ long curve with ~226 control points.
The curve was made from two separate curves that I joined. When I delete the control point at the join one of the end control points disappears. See screenshots.
I’m using version 7.0.20295.18003 (couple weeks old).
Are you sure that point you are deleting is in the middle of the curve? Maybe the curve doubles back on itself and that point you are deleting is the actual end point. If you send a Rhino file, it will be easier to tell.
You could try running crvstart and crvend to make sure the ends are where you think they are.
File with two examples of polycruves… Turn on control points. Delete the control point at the joint (cusp) and the control point at the end of the polycurve is also deleted.
BETA (7.0.20309.6003, 11/4/2020) Joinedcurvedeletebug01.3dm (1.6 MB)