For reproduce this issue follow these steps:

• Create a sign trade that sell a potion (for example speed) or an egg.
• Now add to sign more potion or egg of another type (for example jump, or a normal potion with ID 373)
• You see that you can add different type of potion or egg in a sign that sell another type of potion, but if someone buy the potion it returns the potion type written in the sign.

So the more sign is broken or the buy sign is?

I don't try on other sign, I've tried only on Trade sign

sell and buy not work too

Yes, I can confirm too

Have you tried on the latest build on our CI server?

yes, i use a last. #453

The Trade sign with potion are still broken: screenshot
Latest version used (546) and latest 1.12.1 version of spigot.
(The date of the screen is old, yeah, but the problem is strictly the same)

Issue still up to date with build #532
Server version: CraftBukkit version git-Spigot-da42974-8f47214 (MC: 1.12.1) (Implementing API version 1.12.1-R0.1-SNAPSHOT)

The latest build now allow to trade back potions.
Thank you !

Closing since according to Rakdos8 this is fixed. Feel free to make a new issue if there is still another issue with trade signs.