ID 278552 - IBK_Colour node and VolumeRays node always creates channel "alpha_extra", even when it shouldn't

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Problem summary
IBK_Colour node and VolumeRays node creates channel "alpha_extra"

Customer reported version
nuke.10.0v3

Customer reported platform
windows10

Steps to reproduce
1) Open Nuke
2) Create IBKColour gizmo (tab, type IBK, select colour)
3) Select the Viewer channels dropdown (top left corner, titled rgba)
Result: Only one alpha channel option should appear.
4) View the node (press 1 on the keyboard after clicking node)
5) Select the Viewer channels dropdown (top left corner, titled rgba)
Result: It now displays alpha_extra channel
 
***Same steps as above for VolumeRays node; just swap IBKColour for VolumeRays***

Workaround
Unknown. 

Reproduced by support
-Nuke 10.5v4 - Mac 10.12.3 - Windows 10 - Centos 6.9
-Nuke 10.5v1 - Mac 10.12.3
-Nuke 10.0v6 - Mac 10.12.3
-Nuke 10.0v3 - Mac 10.12.3
-Nuke 10.0v1 - Mac 10.12.3
-Nuke 9.0v9 - Mac 10.12.3
-Nuke 9.0v1 - Mac 10.12.3
-Nuke 8.0v7 - Mac 10.12.3
-Nuke 8.0v1 - Mac 10.12.3

Expected behaviour
Should only display one alpha channel option

Actual behaviour
"alpha_extra"  channel appears after viewing IBKColour and VolumeRays node 
 

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