ID 399169 - Paint buffer transform is causing square artifacts when baking

Problem summary
Paint buffer transform is causing square artifacts when baking  

Customer reported version

4.5v1

Customer reported platform
windows7

Steps to reproduce

1) Open the attached project and the UV view

2) Paint on the UVs and bake

result: square-like artifacts appear:

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Expected behaviour
The paint to be baked as expected 

Actual behaviour
Square artifacts appear when the paint has been baked 

Workaround
Reset the paint buffer using the Zoom Paint Buffer tool

Reproduced by support
This bug has been reproduced in:

4.5v1 - Windows 10 

4.2v1 - Windows 10

4.0v1 - Windows 10 - regression

Unable to reproduce bug in:

3.4v4 - Windows 10 

Earliest version tested
3.4v4 - This issue no longer appears in this version and has regressed