So I think I found a big one, simply said, orders in administration don't work. I click the link (admin.php?p=orders-list), blank page.
Now check this: I go to another language (shop) within the same QC installation, there are not many products in that one, IT WORKS OK. It displays orders from both shops. I go back to the primary language, orders blank screen.
When I erase the db from those products, it works ok. When I generate 4000 products, well.. nope.
This is probably quite easy to fix, once a root cause has been found. Since the bug probably needs a good colonoscopy, I am willing to zip my db files with that enormous amount of products and send it over via e-mail to OpenSolution. Just let me know here and I'll do it at once.