ID 432504 - When a Merge node's output knob is linked to an incorrect channels knob, it updates the knob UI but not the Merge node's output

Problem summary
When a Merge node's output knob is linked to an incorrect channels knob, it updates the knob UI but not the Merge node's output.

Customer reported version
Nuke 12.1v2

Customer reported platform
Windows 10

Steps to reproduce

1) Open Nuke.

2) Create a Merge node.

3) Add an Image/CheckerBoard/Constant to each of the inputs of the Merge node. This is just to help visualise the problem later on.

4) Create a Blur node. This does not have to be connected to the rest of the node tree.

5) On the Merge node, click the Link Menu (the = button) for the "output" knob.

6) In the dialog that appears, type the following expression: Blur1.channels

7) You should see the following error: ERROR: Wrong type of knob Blur1.channels

Ignore the error and press OK.

8) Make some changes made to the Blur1.channels knob and notice that they are reflected on Merge1.output in the UI. However, the result in the Viewer doesn't change.

Expected behaviour
Either the UI should not update when attempting to link the knobs.

Or, ideally, the error would not occur and the result in the Viewer should update as the knobs suggest it should.

Actual behaviour
The UI updates correctly, but does throw an error when attempting to link them.

Even though the knobs in the UI update correctly, the result in the Viewer does not.

Workaround
Unknown.

Reproduced by support

This bug has been reproduced in:
Nuke 12.1v2 - Windows 10 - macOS 10.13 (High Sierra) - Linux CentOS 7 

Nuke 12.0v1 - Windows 10

Nuke 11.0v1 - Windows 10

Nuke 10.0v1 - Windows 10

Nuke 9.0v1 - Windows 10

Nuke 8.0v1 - Windows 10 - macOS 10.13 (High Sierra)

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