Make sure the bug also happen when Details! is the only addon enabled.
This bug is present whether Details! is the only enabled addon or not.

Game and Details! version
Details! version: R9213
Game version: 9.1.5

Describe the bug
Nothing happens whenever you try to change window scale with plus/minus button to the right of the slider.
But if you right-click on slider after you change the scale with plus/minus button - scale change.
So step-by-step:

1. Open Details! options.
2. Click on plus/minus button to the right of the slider.
3. Scale doesn't change.
4. Right-click on slider - scale changed.

Also, if you click RMB on slider, manually write a scale and press Enter - scale doesn't change.
P.S. Change the scale using the left mouse button(manually clicking or drag the slider) on the slider works as it should.

Other Information
Here is small video to show what i mean.
https://www.youtube.com/watch?v=BeyNFgDIvPM

With new update(Details! version: R9688) there is no more buttons plus/minus to the right of the slider.
Slider now scales only by 0.1(1, 1.1, 1.2 etc) and looks that it works ok(not the way I thought but ok).