OK, I have first created a set of new tables with a prefix which I defined in snews.php as per instructions. I used my current snews.php file for this test (copied it in a subfolder and edited the global settings).
Like that I couldn't create new articles - I'd login, create a new article (published) and there would be no article after that (checked the database - it was empty). Since I added some new functions like meta tags mod I thought maybe this mod is a problem since it enables writing information into two new fields, which I didn't create this time in the databse - so I moved the mod and tried again. Same result. I'd create an article and it wouldn't be written into the database.
I had to try it with the current snews.php file so I could determine whether the problem is in it or not. But I was now tired of this not working and I replaced the snews.php with the new one (fresh download).
I was now able to create articles and they would nicely show up immediatelly after being created so it was time to test - I created a new, unpublished article, searched for it, and guess what - it showed up in search results.
What does this tell us? The problem obvioulsy isn't in my modified snews.php file. So where is it? Could it be something server related?