I don't know where is problem - renderer, cloud placement procedure.
Well, if you don't know where it is, why do you claim it is in the weather system? Obviously it matters whether e.g. your AP or the weather system has an issue, no? We wouldn't want to change the weather because your AP is overly sensitive for instance (just as an example).
But, well - now you know, because I told you, no?
If You can't observe problem, it doesn't mean that problem doesn't exists
No, it just means if I go looking and can't observe it, it's likely a problem peculiar to something you are doing and I am not doing or some config you're running but I am not (or a problem related to your hardware which mine doesn't have, though typically that's mostly true for rendering, precious little else I've seen being HW dependent) - it just means that it's not a general problem.
I also believe code is fairly deterministic - if there's instructions in there to interpolate, there'll either be a crash and nothing works, or the instructions will be carried out. But that a non-conditional code-block is simply skipped - that I've never seen.
***
In a general vein - if you go looking for specific bugs in flightsims or search for where the scenery is not developed, I'm fairly sure you'll find plenty in each of them. FSX can look quite hideous as well if you try the right location, it can have ridiculous clouds if you look for the right lighting,... so there's that. I believe trying to create a message based on comparing bugs of one flightsim against well-developed scenery of another is nonsense.
But again - if FSX makes you so much happier - then simply invest some money and use it!