ID 497004 - Custom Environment Light Texture has no Thumbnail

Problem summary
Custom Environment Light Texture has no Thumbnail

Customer reported version
Mari 4.8v1

Customer reported platform
Windows 10

Steps to reproduce

1) Launch Mari and open any project

2) Open the Lights palette and click the Environment Light

3) Add an image to the Environment > Texture > Image property

Expected behaviour
A thumbnail of the image should be displayed:

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Actual behaviour
No thumbnail is displayed:

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Workaround
Unknown.

Reproduced by support
This bug has been reproduced in:
Mari 5.0v1 - Windows 10 - CentOS 7.9
Mari 4.8v1 - Windows 10 - CentOS 7.9 - regression

Unable to reproduce bug in:
Mari 4.7v5 - Windows 10 - CentOS 7.9

Earliest version tested
Mari 4.7v5 - This issue doesn't appear in this version and has regressed