Special brush auto-rotates at each pen- or mouseclick: how to disable

[RoyCoumans]

I have installed the Wacom Intuos Pro and I was experimenting with it. Now, something very annoying is set to my non-round shaped brushes. Each time I click with my pen or mouse on the picture or drawing, the angle of the brush rotates automatically. I have for example a "Lightbeam" brush, which is going into another direction each time I click. I searched over Photoshop brushes, the Wacom-settings. I cannot find anything. How do I turn this of?

[c.pfaffenbichler]

Could you please post a screenshot with the pertinent Panels (Layers, Brush Settings set to »Shape Dynamics«, Options Bar, …) visible? 

[RoyCoumans]

I left my Mac for a while and now it stopped. Just like that. I don't know how.

[c.pfaffenbichler]

Well, post again if it should happen again.