The bug
With 19w42a, dispensers now dispense empty bottles when they're not facing water. This also happens if there's a bee hive or bee nest in front of them that doesn't have honey in it.
This might be an unintentional side effect of the change in 19w42a, or it might be an intentional change.
While it may be working as intended, I find this very annoying, and also counter-intuitive when considering how dispensers work with shears: They don't throw those out when facing an empty hive.