The bug
Right-clicking an area effect cloud with a glass bottle in creative mode gives you a dragon's breath item. Expected would be that you do not get an item, because other actions like the following ones do not give you an additional item.
Right clicking with empty glass bottle on cauldron does not give water bottle
on the other hand ability to pick up buckets was added (see MC-9856)
How to reproduce
Summon an ender dragon with a custom UUID
/summon ender_dragon ~ ~ ~ {NoAI:1,UUID:[I;0,0,0,0]}Summon an area effect cloud with the ender dragon as owner
/summon area_effect_cloud ~ ~ ~ {Duration:2000,Radius:5f,Owner:[I;0,0,0,0]}Right click the area effect cloud with glass bottles
→ ❌ You will notice that you get a dragon's breath item
Linked issues
relates to 3
MC-9856
you cannot pick up buckets of water/lava in creative mode
Resolved
MC-114105
Cleaning leather armor and shulker boxes in Creative lowers cauldron water level and modifies item
Open
MC-269237
Using a water bottle to fill a cauldron or transforming dirt into mud in creative mode gives the player an empty bottle
Reopened
I don't know if this should be considered a bug based on what it is now. You do get honey bottles on creative, you can get fish in a bucket on creative you can use a bottle to get water on creative, and Mojang has fixed bugs that allow these things to happen on creative