ID 199893 - CornerPin node driven by TCL linked expression does not produce correct results in Nuke 9.0v8 and later

Problem summary
CornerPin node driven by TCL linked expression does not produce correct results in Nuke 9.0v8 and later.

After further investigation the issue appears to stem from the use of the following TCL expression linked code:

[sample node channel x y dx dy]

When this TCL command linked through an expression to another node, it will feed back 0'ed out information. This occurs because the image pixel values need to be calculated before the expression accesses the values.

 This is documented in the TCL documentation online.
http://www.nukepedia.com/reference/Tcl/group__tcl__builtin.html#gaf2156ac5f6c8a52407f6282348dfee43

Customer reported version
nuke.9.0v8 and nuke.10.5.5

Customer reported platform
N/A

Steps to reproduce

1) Open the attached file or open your current script that this issue is occurring in

2) Find the [sample node channel x y dx dy] TCL code affected expression values (Expr4 in attached file)

3) Open node that is using the expression linked TCL code and change the values (CPin2D in attached file)

4) View the node that is affected by the TCL code, you will notice that the values have all returned a 0 value (Expr4 in attached file)

Result: TCL expression is causing the linked values to zero out when altered and causing unexpected results (Strobing CornerPin in our example)

Workaround
Avoid using the above TCL code to link sample values between nodes

Reproduced by support

Expected behaviour
The [sample node channel x y dx dy] TCL code should not zero out values when used in an expression

Actual behaviour

The [sample node channel x y dx dy] TCL code zero's out values when used in an expression