P3D v4 First seasonal experience: Strange snow appearance

Hi to all experts,

that's strange: Started some days ago with my first trials at seasonal textures, but all results look very strange so far.

Firstly: I have some experience in using SODE, so many objects which were animated work fine (fence gates, Hangar doors, some small light effects, sound....)
So I know how to use the parametres in "simobjects", "xml" and "sim.cfg".
But my real problems start by trying to add different seasonal textures to a ground polygon and include it into the scenery. Please have a look, maybe someone knows this appearance and how to solve it?!?
Oh, please don't get sidetracked by the snow textures on the treetops, those are models which aren't disabled so far because of other designing work :stirthepo . The seasonal change on them works fine.

Here you can see that the created poly seems to be there, but only snow that appears you can see on the objects which touch the ground - a small white stripe surrounds the lower parts - even the tyres of the user aircraft, the C-130 (red arrows...):

Here another abnormality: The snow, normally awaited to cover the ground, covers most parts of the 3dimensional railwayobject!

Each helping hint is much appreciated!
Okay, a bit confused about this strange behaviour, I want to clear my options about what is possible with seasonal groundpolys generally.

I have built a snow groundpoly, consisting of the base ground poly I've done for the summer season.


My idea: Setting only this polygon to the hard winter season via SODE, but leaving the base poly as it is (summer). By adding a higher layer, I would like to let it appear at hard winter on top of the summer layer. Same with fall and winter.
Is this possible?
I see an issue indeed: Because of the fact to export the file as mdl that is needed for SODE, the earth curve correction is not in use - regarding that big area, it seems to be impossible to prevent flickering, right?
Is there any option to use the exported bgl file by converting it with the GPW that includes the earth curve correction? Is there any alternative for a seasonal visibility of this hard winter bgl? Maybe as an effect?
What are my options to get success nevertheless?
How would YOU solve this problem?
Many thanks in advance.
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