Laggy geometry window

[micheus]

This is not produced by me intentionally. If you remember back in the days of wings 1.0.2, it used blue faces to signify faces that were not exported. Like this.
...
When Wings 2.0.5 or 2.1.5 loads the object, it looks like the one in the previous post.

I see. I didn't knew about that.

Sorry for the delay. I had to download and install the old 1.0.2 and do a test.
You can use what I said in the previous post, but before you need to select the faces (it can be select the entire object, but then back in Face mode) and use Hole [RMB] (remove hole). That will put your model in the condition I was expecting before. Then you can select the internal faces and Bridge them.