You should refrain from fixing this and call it working as intended. For most players, this adds an extra step of "remove the bottle" when brewing lingering potions. The extra time that this takes greatly outweighs the benefit of getting a bottle back.
For redstone users, it is even worse. The bottle being left on the brewer is different than every other ingredient. Since it has to be accounted for, many of us have autobrewers where lingering potions cannot be brewed. I was forced to built a completely separate setup just for lingering potions, and there was no way to make it clockless, so the machine is more prone to errors.
This bug us beneficial, please leave it as is.
I completely disagree with Meri Diana's comment. There is no reason to artificially limit gameplay, especially when the functionality has already been fixed.
You can already transport ocelots and untamed wolves via boats and minecarts. What benefit is there to be obtained from limiting users to moving them using these clunkier methods? You can already attach leads to polar bears and passive mobs like cows, which can never be tamed. You can attach leads to untamed llamas and horses. You can even attach leads to iron golems which demonstrate a level of sentience. Why not ocelots and wolves?
Furthermore, removing this functionality only hurts players, especially those from the younger audience. It's not unreasonable for players to want to make a zoo, or to have a pet that isn't a tamed cat/dog or farm animal. Why would you make it unreasonably arduous to do so? How does allowing players to easily move these creatures to a desired area hurt anyone playing the game in any tangible way?
Confirmed to still occur in 10.2 for Windows 10. Untamed Wolves also cannot have leads attached to them, but polar bears can.
For consistency and fun gameplay, please make it so that all animals can have leads attached to them instead of ruling this working as intended.
Frost walker should activate while riding a horse, because it creates a quicker means of exploration for players who have invested the time to find the enchant. It makes a difficult to obtain reward even more valuable, and creates a very fun experience.
It would be preferable if these changes would be reversed, even if that meant frost walker causing issues while the user is in a boat. A user can take their boots off before getting in a boat. However, if the enchant does not work for mounts, there is no in-game solution.
Feedback from end users can be beneficial. I imagine this is why public comments are enabled on the Jira.
From a functionality point of view, the bottles coming back are not useful, even for users who recycle their bottles. Consider these cases:
1. Your next batch is not lingering potions. If you saved all of your potion bottles from a double chest of potions, you now have 18 extra bottles. This is not enough to brew another double chest of potions, you only need the bottles that you saved from drinking.
2. Your next batch is lingering potions. The bottles are still useless because you need Dragon's Breath, not empty bottles. It's unlikely that a user goes into the end every time they want a new batch of lingering potions. Most of us collect several stacks of breath at a time because of the required effort and inherent threat of the process.
What you have is 18 extra bottles with little to no use every time you brew a double chest of potions. It is only when you brew 3 double chests worth of potions that you see any form of return. But this benefit is outweighed by the detrimental effects of needing to take the time to remove the bottles, the fact that it breaks auto-brewers, and the fact that these bottles need to be stored or managed in inventory for a long time until they are useful.
From an RP point of view, it still makes sense. Dragon's breath evaporates from the ground in just a few seconds, which is observed during the Ender Dragon fight. If the user has to connect the entire bottle to the brewing stand because the breath can't simply be poured into it, it's not unreasonable that the heat from the blaze rod could break or otherwise warp the bottle and render it useless. Since fluid gameplay and fun are more important than complete realism, it can just be assumed that the player character discards these bottles, hence they do not remain in the brewing stand when the process is complete.