ID 416501 - Incrementing with the middle mouse button does not work when having big slider precision

Problem summary
Incrementing with the middle mouse button does not work when having big slider precision 

Customer reported version
mari.4.5v2

Customer reported platform

Steps to reproduce

1) Open Mari and an example project 

2) Go to Edit>Preferences>Misc and make the Slider Precision 10 

3) Go to the Layers Palette and try to change the last digit of the Opacity slider by using the middle mouse button

result: It is not incrementing or it has weird results 

Expected behaviour
It should increment by one regardless of the slider precision 

Actual behaviour
When using larger slider precision, the incrementing is either not working or it is incrementing weirdly 

Workaround
Use smaller slider precision 

Reproduced by support
This bug has been reproduced in:

4.6v1 - Windows 10 - CentOS 7 (MATE)

4.5v2 - CentOS 7 (MATE) - regression

Unable to reproduce bug in:

4.5v1 - CentOS 7 (MATE)

Earliest version tested
4.5v1 - This issue doesn't appear in this version and has regressed