Artemesia: this thing has been going on as long as there have been space marines.
Uncle Arkie: the point was that there is a loophole in canon that would, in theory, permit such a thing. Notice: in canon marines do not burst into flame spontaniously, yet not burn. However, in the Cursed Founding, exactly that happened. Along with a whole spectrum of other highly freaky things. Half of all known chapters founded in the 21st founding came out of it rolling on the Mutations Table, all of whom strain the Inquisition's tolerance for mutants, and some of whom were flat out excommunicated.
And, oddly enough, all this bizzarity is, in fact, canon, feel free to look it up just how messed up it got in Index Astartes.