ID 316501 - ZDefocus introduces RGBA information in completely black pixels

Problem summary
ZDefocus introduces RGBA information in completely black pixels.

Customer reported version
nuke.11.0v2

Customer reported platform

Steps to reproduce
1) Open Nuke.
2) Open the provided script via file>open.
3) View each unpremult node.
Result: Artifacts in areas that were black prior to the ZDefocus.

Workaround
Open the Zdefocus properties and enable mask using the rgba.alpha channel.

Reproduced by support
Nuke 11.0v2 - Windows 10, OSX 10.13, Centos 7
Nuke 11.0v1 - Windows 10, OSX 10.13
Nuke 10.5v6 - Windows 10, OSX 10.13
Nuke 10.5v1 - Windows 10, OSX 10.13
Nuke 10.0v6 - Windows 10, OSX 10.13
Nuke 10.0v1 - Windows 10, OSX 10.13
Nuke 9.0v9 - Windows 10, OSX 10.13
Nuke 9.0v1 - Windows 10, OSX 10.13
Nuke 8.0v7 - Windows 10, OSX 10.13
Nuke 8.0v1 - Windows 10, OSX 10.13
Nuke 7.0v10 - Windows 10, OSX 10.13, Centos 7

Earliest version tested
Nuke 7.0v10 - This issue appears to be in all versions of the product on Windows 10, OSX 10.13, and Centos 7.

Expected behaviour
Black pixels should remain completely black.

Actual behaviour
Black pixels have apparently random RGBA information, noticeable when un-premultiplied.