Texture paint temporary artifact

Hi,
while painting in the uv editor the brushes also paint some kind of transparent rectangle with the size of the brush-circle on top (following and ‘stamping’ itself whereever i apply the brush) that lasts until i save and reload the texture or otherwise refresh it.



But this makes it hard to work with the actual color shades.
Is there any trick to make it disappear?

(Windows 7, Blender 2.78c, geforce gtx 750)