ID 247407 - Output from group nodes can cause shader render errors

Problem summary
The output from group nodes does not display correctly when plugged into the shader.

Customer reported version
3.2v1
Customer reported platform
OS 10.11, Linux RHEL6.5, Win10

Steps to reproduce

1) Open Mari 3.2v1 

2) Create a fresh 'Example Head project

3) Navigate to the node graph and select all the nodes in the diffuse channel backdrop except bottom trans

4) Press [CTRL]+[G} to group

5) Notice the diffuse textures are no longer displayed.

Workaround
If you add in a merge or channel node between the group and the shader, the image should render correctly.

Reproduced by support
3.2v1
Win 7, OS 10.12

Expected behaviour
The viewport should display textures correctly.

Actual behaviour
Users may experience an unable to render shader error.