Inconsistency with regolith and magma heat capacity

This has been in the game for years now, and forms the basis of what's called a "Regolith Melter", which exploits this very fact to convert 20kg/s of Regolith into approximately 22kW of power.

There's actually quite a large number of ways in which matter conversions break the laws of thermodynamics in this game (note, for example, that Mafic Rock has the same heat capacity as Regolith and also converts into Magma), and while the regolith→magma→igneous rock conversion is probably the most egregious, it's also unlikely to ever get fixed for the same reason that other such breaks probably won't get fixed either: the game was difficult to balance around properly conserved energy/heat, and the devs decided that for the sake of playability, they weren't going to.