Krita 2.8 beta 1 (2.7.9.3) latest installer (downloaded tonight) installed on Windows 7 (64 bit)
Cpu Intel 7 - Gpu Geforce Gt 540M

This same bug occurred with the previous installer on Windows 7 (32 bit)
Cpu intel 5 - Gpu Ati radeon 

I have even tested Ubuntu 13.10 - 64 bit (Unity Desktop) and this bug occurs on this platform as well.
Krita 2.9 (pre-alpha) is installed through the Lime ppa by Dmitry (just upgraded today as well).

OpenGL is always disabled (both on Windows 7 and Ubuntu 13.10).

Reproducible: Always

Steps to Reproduce:
1. Fire up Krita 2.8 (beta 1);
2. Open new Custom Document (e.g. 600 x 450 pixel; 300 dpi, white canvas as background);
3. Select no matter what vector shape: e.g. an arrow;
4. Drag this vector shape on the canvas *while* changing its size: you always get black artifacts (spots) on the canvas underneath.

Pay attention: if you save this image as .kra the dots are no longer present in the new image. 
On the contrary, if you save this image as jpg or png all black spots are visible on the new images
Actual Results:  
Black artifacts on the canvas while dragging *and* modifying the size of any vector shape.

Expected Results:  
Krita 2.8 beta 1 should not produce artificats on the canvas while dragging the vector shapes (mostly because they are saved into the new image later...).

To avoid these artifacts later, it looks like you should simply save the image as .kra :-)

Here you can download a video with all my steps:
https://dl.dropboxusercontent.com/u/3095134/BUGS_REPORT/Krita_2.8_beta_vector_artifacts_while_moving_shapes.avi