ID 457824 - Nuke allows you to add an existing channel to a new layer, if you only add one built in channel

Problem summary
Nuke allows you to add an existing channel to a new layer, if you only add one built in channel

If you add multiple channels to the new layer, then New prevents you from adding the existing channels to the new layers

Customer reported version
nuke.12.1v2

Customer reported platform
10.15

Steps to reproduce

1) Open Nuke

2) Create a Shuffle node

3) In the out knob, create a new layer, and just add a single existing layer:

4) Press OK and the layer seems to work as expected. Save the script.

5) Close and reopen Nuke (not script clear), the layer and channel disappear from the Nuke script

Expected behaviour
To not to be able to add a single existing channel. For example if you add two or more, then you get this warning which prevents you from adding it:

Actual behaviour
There was no error, which allowed Nuke to create a channel which it couldn't save

Reproduced by support

This problem has been reproduced on:

Nuke 12.2v3 - Windows 10 - MacOSX 10.14

Nuke 12.2v1 - Windows 10

Nuke 12.1v1 - Windows 10

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 - MacOSX 10.14

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