Using Audacity 2.1.3-alpha-Apr 4 under Vista Home Premium SP2:
If I select the Envelope Tool and then switch to a different cursor without actually using the Envelope Tool, the cursor changes as expected. If I use the tool (create, move or delete control points), then switch tools via a Function Key, the Envelope Tool cursor remains on until I either move it out of the track display area or do something which forces a cursor change e.g., change the select range, move the cursor into a label and select or edit it, etc. Just moving the cursor through a select range with e.g., the I-beam tool selected doesn’t cancel the Envelope Tool cursor, even though the I-beam would have changed to a finger while at the boundary.