Microsoft Docs says:
The behavior of cpobj is unspecified if ……, or if classTok does not represent a value type.
But ECMA 335 says:
If typeTok is a reference type, the cpobj instruction has the same effect as ldind.ref followed by stind.ref.
Which is correct?
If we look through the previous editions of ECMA-335, we find that the 3rd edition changed the wording to specify:
If typeTok is a reference type, the cpobj instruction has the same effect as ldind.ref followed by stind.ref.
In editions 1 and 2, the wording matched that on MSDN.
Therefore, I think it's safe to conclude that ECMA-335 6th edition is correct, and MSDN is out of date.