On Mac OSX, in Mari 3.1v2 and 3.1v3 certain tools such as Blur and Clone stamp, work in the linear colourspace regardless of channel depth. As a result, blurring or cloning an image in an 8-bit sRGB channel creates mismatched values based on the channel.
Mac OSX only supports up to OpenGL 4.1 whereas Windows and Linux presently support up to 4.5. This means that Mac OSX is missing features like compute shaders that Mari uses for Blur and Cloning calculations.
Go to Mari>Preferences>GPU> And untick 'variance maths'
Figure 1) Above is the current state of these tools, below after unticking 'variance maths' we see the tool working in the right colourspace