Hi Umberto, thanks for the reply. First I want to say that in no way I meant for my post to sound like I was really dissatisfied with the products, because I am not. I really love them and keep buying them. Seeing as how this is the internet I know that it is hard to tell what the tone of someones post is.
You asked for some examples of sceneries that I have that have custom ground textures that don't do what I was explaining. Here they are: FlyTampa St. Maarten, Imaginesim KCLT and TJSJ, Sim Giantes Gran Canaria International Airport, Aerosoft Madeira X, Aerosoft German Aiports 2, BluePrint KDAL. Although the BluePrint KDAL I removed the photoreal ground because it didn't blend with the default scenery very well. I don't know what the ground resolutions of these are compared to FSDT's are, and off the top of my head I can't remember if they include the ability to show the rain effect.
Anyways, I wasn't sure if there was a work around or a way to get these gound tiles to stay loaded for a longer time, but after reading your reply I guess not. I feel better knowing that I am not the only one who sees this. From a users end would or could I get a better result if I took the time myself and converted the ground tile textures into .bmp's, joined them, added the masks, and compliled them into a single .bgl. The reason I ask is that I have made some custom ground tile textures to use as airport backgrounds that are high res, using a tool like SbuilderX, that displayed under an airports scenery. Although, I have never made the runway or taxiway textures the backgounds looked good under the airport file and they stayed loaded.
I know that I am way out of my league, and do not understand a lot of scenery design, but I thought it would be worth asking. If not, no big deal. It's not a deal breaker for me. I love FSDT's sceneries a lot and will continue to pruchase.

Regards,
Sean