Create Standard Delegate with Update Authority?

[vfr292]

Hi,

Using a token's update authority I'm running:

  await delegateStandardV1(umi, {
    mint: mint.publicKey,
    tokenOwner: owner.publicKey,
    authority: update_authSigner, //note update authority
    delegate: standardDelegate.publicKey,
    tokenStandard: TokenStandard.FungibleAsset,
  }).sendAndConfirm(umi);

But getting an error:

IncorrectOwner: Incorrect account owner

When I use the tokenOwner's authority the error is resolved. I'm confident I have the update authority as I can use it to update the token. From the DelegateStandardV1InstructionAccounts (see below) it looks like I should be able to use the update authority:

    /** Update authority or token owner */
    authority?: Signer;

Is this a problem/bug or am I missing something? This is my first Metaplex project. Please let me know if more code would be helpful or if there is anything else I can provide.

Thank you :)