Denoised pass + Alpha = different result Tweet

[KeeWe]

Can someone explain me why I am getting different results when using the AI denoiser with an alpha? Attached you can see the the 2 seperatley rendere layers, the teeth are the denoised pass, having a jaggy alpha. The rendered beauty of the teeth with noise works fine.

Also: why do I have to set the alpha to unmultiplied for the denoised pass while the beauty just works fine with slpha set to straight?

Isn't there a way to just render one denoised beauty pass instead of the noisey beauty AND the denoised pass?