last edit date needs to be a discrete / manual value....not a function like NOW().
When opening a file, that function wil update to current time.
All MS products work that way
one way you could do this in shapesheet is
user.now = NOW()
actions.updateLED = setf(getref(actions.updateLED.checked),if(actions.updateLED.checked,0,1))
actions.updateLED.tag ="update last edit date"
user.LED = if (actions.updateLED.checked, user.now, NA)
use the user.LED as the cell for the field to be displayed.
right click shape...select the "update last edit date"....will see checked and value update.
repeat and deselect to turn off (otherwise the same problem again).