Paloth, I read your post again and I'm not sure if I understood correctly. You wrote you are painting on blob objects. Blobs as in "metablobs"? If so, did you bake them? If not, I would advise you to do it.

I normally have my mini-preview window without automatic update. I found that, at least in my case, the system tends to be more stable if the mini-preview is inactive while I'm working with boolean objects or metablobs. This is also true, although to a lesser extent, if I'm working with heavy and interactive scene changes, like the ones that could result from ecosystem painting.

Bruno, 64 bit systems also have the same warning.