I have stumbled across an annoying problem in slab6.
See, I was using it normally. Then, there's this block:
http://filesmelt.com/dl/blocks.png
It's the stray one. The problem is, I can't delete it. It seems purely graphical, without a presence considered by slab6, I can even place blocks through it and delete those blocks, but this one just won't go away. What's also weird about it is that it only has 3 visible faces. It might not seem like much, but it's particularly annoying seeing this in game.

Has this happened to anyone else?

will you upload the file somewhere? i'm not sure what you're talking about but i want to find out

Alright, I'd just rebuilt the model and replaced the screwed up one when I saw your comment.
I managed to recreate the glitched blocks though, it has something to do with pressing insert to place a block when your view is inside another block.

http://filesmelt.com/dl/screwedupsemi.kv6

They're around the tip of the bayonet, just try and get rid of them.
Btw, that's not my gun, the original was made by MasterParadox and I added the scope and bayonet. I can find and link to the thread if you want the original gun.

Whoa, I just downloaded the file I hosted, and that is not what it should look like.
There was supposed to be one or 2 white blocks by the blade, but I guess the messed up blocks screwed up the file and messed up everything else. Wow.
But I'm sure there are some of the mysterious glitch blocks in there anyway.

Edit: yeah, there must have been some corruption. But if you look at the gun from one of the sides, the whole thing is messed up and there are a ton of the glitchy 3-faced blocks you can't delete.

now i see what you mean about the blocks

i saved as kvx then back to kv6 and they went away

Oh nice
Okay

Yes, this happened with the UH-1 I was making.