The bug:

When brewing a single Dragon Breath no glass bottle is returned to the player. When brewing 2 or more a glass bottle is returned to the player as expected.

How to reproduce:

1. In a brewing stand place 2 (or more) Dragon Breath in the input slot and a single awkward potion.
2. With 1 blaze powder brew one lingering potion.
3. Note the glass bottle is dropped in the world.
4. Brew another potion using up the last Dragon Breath
5. Note that no glass bottle is dropped in the world or retained in the inventory of the brewing stand.

Expected behaviour:

A glass bottle is retained in the input slot or dropped into the world after brewing the last Dragon Breath.

Many thanks, please let me know if you need any more info.