ResourceObj::operator new[] calls ResourceObj::operator new (non array version). In debug builds, each resource object will be initialized with set_allocation_type() (which is correct). What is not correct is that the constructor (and thus) set_allocation_type() is called on the array itself (which is not a ResourceObj). This initialization will be partially overwritten by the header that keeps track of the array size. When the array destructor later is called, it will also chain call the non-array destructor. In debug builds the verification of _allocation_t[0] will fail as it has been overwritten by the code that keeps track of the array size.

The following assert will fail:
assert(~(_allocation_t[0] | allocation_mask) == (uintptr_t)this, "lost resource object"); 

The reason that it has not been detected is that no one uses ResourceObj::operator new[] on resource objects with C_HEAP storage.