Recently died to the afterburn of a Mekanism (1.12.2-9.8.3.390) flamethrower, and when my grave overwrote a Pixelmon (7.2.2) Lansat berry block that was there before, the grave that spawned belonged to "M4thG33k" which I believe is the name of the Tomb Many Graves developer.

I obviously could not access the grave. since the server didn't believe it belonged to me and my items were effectively voided.

This happened on a private server of four people, none of whom were M4thG33k.