Something got seriously messed up with envelope API.
This script should move selected point to start of time selection but it doesn't.
Example project here
Code:
local envelope = reaper.GetSelectedEnvelope(0)
local p, t, v, shape, tension, s = reaper.GetEnvelopePointEx(envelope, 0, 1)
reaper.SetEnvelopePointEx(envelope, 0, 1, 7, v, shape, tension, true, true)
reaper.Envelope_SortPointsEx(envelope, 0)