When a Merge node is carrying multiple passes in through the B input, they are not correctly interpreted into Merge node's channels knobs. Only the A input passes will be added to the A and B channel knobs within the Merge node.
Although the passes exist within the 'other layers' option area of the channels knob, they should exist with the top layer passes. This inconsistency has also been discovered to cause issues with Merge operations such as stencil which are not correctly handling these input passes.
Note: This issue only occurs with the Merge2 iteration of the Merge node and not present in the original Merge node.
Customer reported version
nuke.11.3v4
Customer reported platform
centos7
Steps to reproduce
1) Read in an exr image that has multiple channels
2) Create a Constant node
3) Create a Merge node
4) Connect the 'B input' of the Merge node into the multiple channel exr image, and the 'A input' into the Constant node
5) Within the Merge node properties, view the accessible layers through the 'A channels' and 'B channels' knobs
Result: multiple passes not passed through to channels knobs from the 'B input'
6) Switch the Merge inputs by selecting the Merge node and pressing 'shift+x'
Result: When switched to 'A input', the passes carry through correctly to the channels knobs
Expected behaviour
The 'B input' of the Merge node should carry through the passes from upstream and be accessible through the A and B channels knobs
Actual behaviour
The 'B input' of the Merge node does not carry through the passes from upstream.
Workaround
It is possible to using the AddChannels node to add in the channels from the B stream to the A stream before the Merge node. (although for several passes this can be a tedious process)