Terrain wont change texture 0.7.0.6

[Fatboymart]

I have a basic oval track. I have X2 open end tracks which blend in to make look like run off area's.

I have used the auto terrain and fill option on all three tracks.

I have selected terrain nodes and joined where applicable.

I have used the "fill" option where also applicable to form wide open terrain which will be a big lake.

My problem is this:

I have selected a single default grass material for all terrain just to get something down.

I am now at the stage where I want to make changed to the grass material at various locations.

I can select all terrain and apply a new primary material (example default grass 1 too default grass 2).

But what happens is a proportion of the selected terrain will take on the default 2, but a large area will remain default 1. I have made shore all relevant terrain is selected.

If I then go to default 1 on its own and try and change the primary material, nothing happens. default grass1 still remains.

I have also noticed that if I select only 1 "FILL" which might have nothing that I am aware of in common with any other "FILL" from a different location on map, and then go and change nominated material - All of the area's which I have used the "FILL" option change to the new material although I did not knowingly select them for change.

To sum up

Why can't I remove a primary material and replace it with another default of my choosing (default terrain materials). It would appear that Grass 1 will not allow me to replace it for some reason.

BTW

I have read the help file and cannot find any error in my selection/de selection of materials.

Thanks