Observed:
If the player is crouching, and has binoculars in hand, then attempts to lower the binoculars, an unexpected weapon swap animation sequence starts.
Player swaps to primary weapon, then lowers that, then raises it again, then swaps back to binoculars.
If the player is standing, attempting to lower binoculars has no effect.
If the player is prone, the player stands upright (see issue #5817), then swaps to primary weapon, then lowers that, then raises it again, then swaps back to binoculars.

Expected:
As with standing, attempting to lower binoculars when prone or crouched should do nothing.