Core Lava has always been this way. That is vanilla functionality.

hmm must've been update that changed that in vanilla. we (me and my friend) used to gather from the cores all the time, including your frackin planets, was very useful in getting liquid protocyte and stuff if we got lucky. i think it stopped working in the last year or two (we take long breaks)
Anyway, thank you for the answer and this mod. time to do more science!

No, you collected *lava*, not *core lava* they are two different liquids. We swapped lava cores back to using Core Lava because of how exploitable it otherwise is (vanilla already used Core Lava, we simply changed it back to default), on starter worlds. You'll note other liquids will work just fine.