This is how I get into trouble.
Select an array formula or a portion of it, hit F9 to display the evaluation, copy the evaluation, select a cell and paste the evaluation.
This way, when going back to the formula bar, I have found no way of getting the array formula back except doing undo. However, undo erases the pasted evaluation. So, the net result is just a waste of time.
To paste evaluation, after copying, one needs to hit ESC or Ctrl-Z to get the array formula back first and then paste. Otherwise, you either lose the pasted evaluation or the array formula. Can't have both of them at the same time.