Drawing tools

I am really loving the D20pro program. It is quite amazing in how it speeds up play and combat and keeps track of all of the buffs for us. I am struggling though with trying to use the program as a blank battlematt canvas with the drawing tools. From what my tests seem to have show so far is that if you use the manage tile option to create a tile, that no matter what you do, you cannot have any tile sitting on top of either a colored square or a square that has been colored with a texture (such as a grass texture) that you have made with the tile painter or the color painter. You can do this with other tiles that you create but if all you want to do is put some tree tiles on top of a textured or colored map (such as a grass field), this cannot be done. What happens is the tile stay's behind the grass texture or the colored texture and cannot be brought to the front on the map with the move to front or send to back feature that the manage tile tool has. you can use the show and sink buttons to show the tree tile but it will remove what was behind it and replace it will a white tile background now under the tree till. I believe this might be a bug but unless I am doing something wrong it really limits how creative of a map you can make front scratch from within the program. I hope maybe this could be a simple quick fix to remedy this or if I am doing some thing wrong that someone can explain the steps for me.