I regard this as a bug and it is logged as such http://bugzilla.audacityteam.org/show_bug.cgi?id=208 .
I agree it needs thinking about, but I note that EQ in 1.3.5 and 1.3.6 don’t remove envelope points - what was the sea-change in EQ (or some other change) that forced the removal of points?
Can you manage with Effect > Bass and Treble, which does not remove control points?
The only way I can think of to restore control points is to open the autosave temporary project file (assuming you add the points after opening the project), copy the envelope points that look like this:
Interesting to learn this is something Audacity might yet build into a future release.
If it is so simple to adjust the autosave file, then I guess it should be fairly straightforward to code similar readjustments automatically - perhaps via a control/button.
Here’s to the next upgrade.
And thanks once again for such a speedy and helpful response,