ID 376331 - Broken UI Intensity slider

Problem summary
The Intensity UI slider in the Select Color>Picker menu is not moving as expected

Customer reported version

4.2v1

Customer reported platform
windows10

Steps to reproduce

1) Open Mari

2) Open the Select Color menu

3) Move the Intensity slider. The slider is not moving correctly

Workaround
Unknown

Reproduced by support

This bug has been reproduced in:

Mari 4.2v1 - Windows 10 - CentOS 7

Mari 4.1v1 - Windows 10 - regression

Unable to reproduce bug in:
Mari 4.0v1 - Windows 10 - CentOS 7

Mari 3.4v1 - Windows 10 

Mari 2.6v5 - Windows 10 

Earliest version tested
4.0v1 - This issue no longer appears in this version and has regressed

Expected behaviour

Slider to move accordingly

Actual behaviour
Intensity slider does not move as expected