Strange .... I work for me, but I just updated my mods 1.8.4 building pack and 1.7.2 Asset pack
You're right, it totally works.
I have been loading other saves without closing the game first.
Every time I load a game now, I close the game, re-open, enable the MODS and then load game...
It's quite an effort, and I hope the developers fix this very manual method of activating MODS.
But it's worth it because your MODS are really amazing. Especially your Surviving Mars ones.
Thank You for your awesome work.
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