While trying to find the memory leak on my curve, I ended up deleting and installing a couple of 3rd party themes. When I finally figured out these were definitely the culprit, I deleted them for good.
Today, I temporarily reinstalled one just to monitor the memory drain for a while. It happened to be the one that I was using before and had installed right after upgrading my OS to 4.5. (yes, it was advertised as a 4.5 theme).
I was quite surprised to see it installed exactly as I had it before. Icons in the same place, using the same wallpaper (one of mine), even the "Unused" folder that I create with each theme to move those icons I would like to see dead (Facebook? Seriously? What am I, fourteen?).
Which has led me to conclude that deleting themes leaves something behind. Some sort of BB equivalent of an INI file.
I think that there is a folder that stuff is stored in. plug up to your dm and i think its called a content store folder or something, but clear that and that should take care of your problem.
Actually when you connect to bb desktop manager there will be an application loader removal program the themes should be listed under that for removal, and it should not delete anything else.