ID 376388 - Using certain expressions on a Text soft-effect will cause the cache buffer to continuously rescale and cause flickering in the Viewer

Problem summary
Using certain expressions on a Text soft-effect will cause the cache buffer to continuously rescale.

This may cause flickering in the Viewer on a multi-track project.

Customer reported version
Nuke Studio 11.3v1

Customer reported platform

Windows 10

Steps to reproduce

1) Open Nuke Studio

2) Import two image files. In this example, the issue has been reproduced using a still frame EXR and a greenscreen footage MOV file.

3) Drag your background footage onto the Timeline.

4) Create a Blend Track by right-clicking the Timeline and selecting New Track > New Track Video Blend > Over.

5) Put the greenscreen footage on the newly created Blend Track.

6) Apply and Chromakeyer soft-effect and create a key on the footage.

7) Apply a Text soft effect and, in the 'message' field, type [frame]

8) Highlight the text in the message field and adjust the 'font size' knob. The cache buffer should now start to rescale continuously and the image in the Viewer may start flickering.

Workaround
It appears that setting the following environment variable will stop this behaviour:

FN_DISABLE_TIMELINE_DISK_CACHE=1

Reproduced by support
This bug has been reproduced in:
Nuke Studio 11.3v1 - Windows 10 - CentOS 7 - macOS 10.13 (High Sierra)

Nuke Studio 11.2v1 - Windows 10 - CentOS 7 - macOS 10.13 (High Sierra) - Regression

Unable to reproduce bug in:

Nuke Studio 11.1v6 - Windows 10 - CentOS 7 - macOS 10.13 (High Sierra)

Earliest version tested
Nuke Studio 11.1v6
- This issue no longer appears in this version and has regressed

Expected behaviour
The Timeline should cache correctly and the image should be displayed without flickering in the Viewer.

Actual behaviour

Using certain expressions on a Text soft-effect will cause the cache buffer to continuously rescale. This may cause flickering in the Viewer on a multi-track project.