[LegionMammal978]

Such behavior violates C89 (they later made it unspecified, likely to match the divergence):

> If size is zero and ptr is not a null pointer, the object it points to is freed.

It also violates every version of the SUS and POSIX up to Issue 6 (they made it unspecified in Issue 7):

> If size is 0 and ptr is not a null pointer, the object pointed to is freed.

Going down to at least the 3rd edition of SVID:

> If size is zero and ptr is not a null pointer, the object pointed to is freed.

[kazinator]

What's obvious about all those Unix-related specifications is that they are not of BSD lineage.