ID 280502 - Python callback prevents read nodes from setting correct colorspace when the read node has other nodes below

Problem summary
Python callback prevents read nodes from setting correct colorspace when the read node has other nodes below

Customer reported version
nuke.10.5v4

Customer reported platform
centos6

Steps to reproduce
1. Open attached script and reconnect write nodes with attached frame
2. Save script and close Nuke
3. Open Nuke
4. Run the following in the script editor:

def callback():
   node = nuke.thisNode()
   width = node.width()
   print node
   print width

nuke.addOnCreate(callback, nodeClass="Group")
nuke.scriptClear()

5. Open the saved version of the script with the updated file paths
Result: Read3 will display with (Cineon) on node thumbnail and the colorspace on node can appear as either set to 'default (ACES - ACEScc)' or 'Cineon'. The image will display in Cineon colorspace and on occassion will state Cineon in the thumbnail, but display as ACES - ACEScc.
- If you view the node and move the mouse over the viewer the node will update back to ACEScc in properties, viewer colourspace and on the node thumbnail.

Workaround
Unknown.

Reproduced by support
Nuke 10.5v4 - OSX 10.11.6
Nuke 10.5v1 - Windows 8 - Result: viewer won't update unless your viewing the bottom of the node tree, instead of just the read node itself
Nuke 10.0v1 - OSX 10.11.6
Unable to test prior to Nuke 9.0v9 due to changes to OCIO and how project settings are handled. See comments for more info. 

Expected behaviour
Colorspaces to be set correctly and display correctly in viewer

Actual behaviour
Python callback prevents read nodes from setting correct colorspace when the read node has other nodes below