That isn't transparency, it's Z-sorting issues. For this, you have three options:

1. Do not enable the transparent flag.
2. Avoid using textures with alpha channel in it.
3. Add a material with a simple shader effect in it (this requires at least commercial edition). I don't know shaders, but I think one of the instructions is "zwriteenable = on;" (without the quotes) and there was at least one other one.

If you want a transparent part, use that transparent part as a separate entity.