Hi, for most problems in P7,  the culprit is usually the graphics cards drivers. Both the nVidia and ATI drivers have caused problems for P7 because of it's newer OpenGL preview. The first test is to try the older SreeD setting under the  'render settings:preview' tabs. If these problems stop, then your graphics card/drivers are the cause. Try installing the latest drivers following your manufacturers instructions.
PS...  you can first try switching  from 'hardware' to 'software'  for the accumulation buffer which as also located in the 'render settings' preview tab.

Regards,