Type of Issue/Request (Bug / Crash / Suggestion / Translation / ...):

Bug

Version of the mod or build number:

0.5.1

Are you a Single Player, a Multiplayer Client (You are a player in a server) or Server Side?:

Single Player

Minecraft Version (1.9.4, 1.10, 1.10.2, 1.11.2...):

1.12.2

Description (or what were you doing when it crashed):

Not necessarily crashed, just odd effect when using the two mods.
I was using Extra Alchemy with Combined potions. I tried to use a combined potion (in this case, fire resistance, jump boost, and regeneration) with the combining effect from your mod. However, that resulted in only one item getting the extended duration.

Pastebin of the log (fml-client-latest.log from your instance/logs folder):

https://pastebin.com/DEaWmxWK (placebo did some log spam, so i cut all that out)

ModPack (or list of mods via Pastebin. If using a modified modpack, write BOTH the modpack AND the link to the full mod list):

https://pastebin.com/cmFhuQ8Q

Pastebin of the config file (extraalchemy.cfg from your instance/config folder):

https://pastebin.com/hQ4rwQec

OS and Java version (Java8 + Windows10 / Java7 + MacOS / ...):

Windows 10 + Java 8

Other information that you think might be useful:

Think its related to what the last potion combined was.

Hello, can the 1.12.2 forge version source be uploaded here?

Thanks in advance.

Potion combining is not meant to be used with multiple effects. I'll add a check next version to prevent them from combining