Inside of mesh is see through when trying to make a hole? I am trying to make a hole in this mesh:



but when I delete the vertices/faces, this happens:



How can I delete the top and bottom in the middle without this happening? I want the inside to look like how it does on the outside, not look like there is stuff missing.

What it looks like when rendered:
After finishing your model do the following:


press A to select the entire mesh
press W, select remove doubles
press CTRL + N to correctly orient the normal ones
press A to deselect everything
exit to object mode and export following the instructions


NOTE:

your blender is probably damaged, or some addon is causing you conflicts

I made the following example I exported it to unity, roblox and U4, and it worked well, it is possible to say that the risk of having a bad problem or having problems is greater because I use my own compilation and fork of blender to work, which I have modified in many parts, if you use a release version of blender.org you shouldn't have any major problems than the ones I could have