ID 469264 - Ptex map exports with incorrect texture data

Problem summary
Ptex map exports with incorrect texture data

Customer reported version
Mari 4.7v2

Customer reported platform
Windows 10

Steps to reproduce

1) Create a New Project, using the attached "PtexSphere.obj" file as the geometry

2) In the Ptex Import or Creation dialog, change the Worldspace Texels value to 100 and click Ok

3) Apply paint to the sphere using the Paint Tool, then press B to bake the texture

4) Select the Base Layer in the Layers Palette, right-click it and select Export > Export Selected Layers, then navigate to a suitable location and click Export

5) Hide the Base Layer by clicking the

​ icon, then create a New Layer by clicking Layers > Add New Layer

6) Right-click the New Layer and select Import > Import into Current Layer

7) Navigate to the previously exported .ptx file and click Import. Then click Ok in the Ptex Texture Import: Face Texture Resize Options dialog

Expected behaviour
The imported texture should match the originally painted Base Layer

Actual behaviour
The texture is now incorrect, some mesh faces are filled with a single colour instead of the painted texture data

​​​

Workaround
Unknown.

Reproduced by support
This bug has been reproduced in:
Mari 4.7v2 - Windows 10 - CentOS 7.7
Mari 4.7v1 - Windows 10
Mari 4.6v4 - Windows 10 - CentOS 7.7 - Regression

Unable to reproduce bug in:
Mari 4.6v3 - Windows 10 - CentOS 7.7

Earliest version tested
Mari 4.6v3 - This issue doesn't appear in this version and has regressed