Well the masterpage is not changed. As for the page, I did some exerimenting, but later I reseted it to the site definition. Additionally I created a new page and tested the webpart there, no change. I don't know if that's relevant but the folders in the library have unique permissions and do not inherit from the library. This is for preventing some users to read some of the content. But as administrator I can see all the folders.

Thanks @Mike. I tried that but with no success. I even recreated the view witch I use but the result was the same. And the error isn't even consistent. I've set an item limit of 30 and while the first 30 would have this issue, the next 30 would be ok and the next ones would be scattered again.

link - here you go. This is the list view webpart in question and actualy it is using a flat view (without folders) but the issue is the same. Another interesting thing is that i have another webpart of another library next to it and it shows ok.

So a workflow will start on upload of a file, but not on Save in the edit form unil the item is approved. I find that strange. Doesn't the upload operation change the approval status to pending. Also I can start the workflow manualy.