ID 420325 - ZDefocus adds noise to the Alpha channel

Problem summary
ZDefocus adds noise, both positive and negative pixel values, to the Alpha channel.

Customer reported version
Nuke 11.3v6 

Customer reported platform
Linux

Steps to reproduce

1) Open Nuke and open the attached script. It contains the following nodes:

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2) The following shows the Alpha channel and the Depth channels, when viewing the Crop node before applying the ZDefocus:

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3) Apply a ZDefocus node.

4) View the output of the Grade node. The multiply and gamma knobs have been set to 10 to make the noise visible.

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Expected behaviour
The Zdefocus should not be adding any noise to the Alpha channel.

Actual behaviour
The ZDefocus adds noise to the Alpha channel.

Workaround
You may be able to remove the noise by creating a Clamp node, and setting the 'minimum' knob to the lowest possible value where it is higher than the pixel values of the noise. The 'MinClampTo' knob will also need to be enabled.

Reproduced by support

This bug has been reproduced in:
Nuke 12.0v3 - Windows 10 - CentOS 7 - macOS 10.13 (High Sierra)

Nuke 12.0v1 - Windows 10

Nuke 11.3v1 - Windows 10

Nuke 11.2v1 - Windows 10

Nuke 11.1v1 - Windows 10

Nuke 11.0v1 - Windows 10

Nuke 10.5v1 - Windows 10

Nuke 9.0v1 - Windows 10

Nuke 8.0v1 - WIndows 10

Earliest version tested
Nuke 8.0v1
- This issue appears to be in all versions of the product