(turtle module has no relation to IDLE other than also using tkinter.  The fact that turtledemo can be run from IDLE is incidental.)

3.10.0rc installed on Win 10.  I first clicked randomly and never saw a missing 'release'.  I noticed that the turtle occasionally jumped to where I clicked, with 'start n' being printed.  I realized that I must have moved the mouse at least a pixel between click and release, triggering a move event.

I then did multiple click-drag-releases.  I am not sure if I ever saw a missing 'release', but sometimes saw an extra 'start' as I released, especially when releasing while moving the mouse.  EP's comment explains this.  A subsequent click and drag prints no 'start' (which really means 'pen down') because the pen was already down.

I see two possible issues:

1. https://docs.python.org/3.9/library/turtle.html#using-events talks about events 'on this turtle'.  Should that mean clicks anywhere on the screen or just literally 'on' the turtle image.  If there were multiple turtles, should 'anywhere on the screen' be 'on' all' of them?  The meaning of 'on' is turtle-specific, so this might be a turtle bug, depending on the intention.

2. The OS sends its graphics screen mouse move events corresponding to the physical mouse being moved.  There are available to tk.  ondrag is supposed to only notice those after button press (and by implication before button release).  In other words, while the button is down.  There should be not be drag events after the release event.  This might be a turtle bug, but could be in tk or even the OS mouse driver