ID 484648 - channel hauling for channel relationships is broken

Problem summary

Channel hauling for channel relationships is broken.

Customer reported version
modo.15.1v1

Customer reported platform
11_big_sur

Steps to reproduce

1) Download and open the attached scene file. 
2) Select the Relationship: Position to Sphere:Position node.
3) Left-click and drag on the HUD in the 3D viewport and notice that nothing happens.

Expected behaviour
The channel should be adjusted.

Actual behaviour

Nothing happens.

Workaround
Unknown. 

Reproduced by support

This bug has been reproduced in:

15.1v1 - Windows 10  -regression

Unable to reproduce bug in:
15.0v3 - Windows 10

Earliest version tested

15.0v3 - This issue doesn't appear in this version and has regressed.