[Rendar]

Lost 1823 Murai.
Lost 1 Alga Plume.
Lost 1 Small Spatial Core.

So upon death, you can lose spatial cores. Spatial cores that you worked your butt off for, this seems like it isn't intentional since you can't actually trade them with other players.

[Ryu-Kazuki]

I reported it back on the old forums, didn't know if it got fixed, but;

Sometimes when you lose a core from a battle, it appears in Richeous' shop and you can buy it from him for 0 murai, regardless of size.

[Neus]

This isn't a bug.