ID 271831 - Expression links to metadata do not update values accurately

Problem summary
Expression links to metadata do not update values accurately

Customer reported version
nuke.n/a

Customer reported platform

Steps to reproduce
1. Open Nuke
2. Open customer script
3. Reconnect footage
4. Open Read1 and view metadata 
5. Look at 'exr/focalLength' and change frames within the in and out points
Result: 'exr/focalLength' value changes
6. Open Camera1 properties
7. Go to projection tab > right click focal length > edit expression > notice the user has expression linked to the 'exr/focalLength' metadata
8. Scrub up and down the timeline
Result: Focal Length in Camera 1 node updates to resemble metadata
9. Play the timeline
Result: Camera does not update based on focal length value in the viewer

Workaround
Unknown.

Reproduced by support
Nuke 10.5v3 - OSX 10.11.6 - RHEL 10.5v3
Nuke 10.0v5 - OSX 10.11.6 
Nuke 10.0v1 - OSX 10.11.6
Nuke 8.0v6 - OSX 10.11.6

Expected behaviour
Expression linked values to accurately match the metadata they are linked to

Actual behaviour
Expression linked values did not accurately match the metadata they are linked to