The ultimate culprit lies in the material handling of the cloud shader.
Go to this folder:
FSX\ShadersHLSL\misc
There you will find a file called SwarmCloud.fx. Make a backup copy of this file somewhere. (as always no crying if you don't do this step)
Open the original SwarmCloud.fx in notepad or wordpad and then look down about 20 lines down from the top. You will see this entry:
bool NewMaterialUsage = true;
Change its value from true to false. Make sure to keep the semi-colon.
Save and close the file.