ID 501884 - The last frame of Blend track is offset by 1, unless the blended track items start at frame 0

Problem summary
The last frame of Blend track is offset by 1, unless the blended track items start at frame 0. 
This issue can be seen when scrubbing forwards through the timeline, but not when scrubbing backwards. The offset seems to only occur in the Viewer, and cannot be seen after rendering the sequence.

Customer reported version
Hiero 13.1v1

Customer reported platform
CentOS 7

Steps to reproduce

1) Open Nuke Studio.

2) You will then need to import two images (File > Import File(s)...). Two example image sequences are attached.

3) Add the two image sequences to the Timeline, on separate tracks. Also ensure that the track items are placed on any frame, other than frame 0.

4) Click the Blend 

​ icon on the topmost track.

5) Scrub forwards through the timeline to frame 5. Notice that the Blend track is offset by 1 frame:

​

Expected behaviour
The correct frames should always be displayed in the Viewer, when using Blend tracks.

Actual behaviour
The last frame of Blend track is offset by 1, unless the blended track items start at frame 0. 

Workaround
There are a few different ways to update the Viewer, in order to see the correct result:

Reproduced by support
This bug has been reproduced in:
Nuke Studio 13.1v2 - Windows 10 - Linux CentOS 7 - macOS 11.6 (Big Sur)
Nuke Studio 12.0v1 - Windows 10 - Linux CentOS 7 - macOS 10.13 (High Sierra) - Regression

Unable to reproduce bug in:
Nuke Studio 11.3v6 - Windows 10 - Linux CentOS 7 - macOS 10.13 (High Sierra)

Earliest version tested
Nuke Studio 11.3v6 - Windows 10 - Linux CentOS 7
- This issue doesn't appear in this version and has regressed