From a standpoint of consistency, this behavior does not make any sense. You should not be able to still be "zoomed in" without actually looking through a spyglass, as the disappearance of the overlay before the spyglass zooms out implies.

Adding to this, whenever the player uses the spyglass, the overlay starts out small and zooms in. This same effect could happen in reverse as the player stops looking through the spyglass, to be consistent.