Automatic foreground color and background colour swap

[Laiserl]

The foreground colour and background colour always change automatically. The colour is changed with each brush stroke. This means that if the foreground colour is red and the background colour is blue, the first brush stroke will be red, the next brush stroke will be blue and the next brush stroke will be red and so on.

[c.pfaffenbichler]

Could you please post screenshots with the pertinent Panels (Toolbar, Layers, Brush Settings, Options Bar, …) visible? 

In particular the »Color Dynamics« in the Brush Settings Panel.