Editor is utterly broken for me and I can't fix it.

I've been struggling with the editor for a few days with no luck, but for some reason, it's just broken for me. The game has all the memory in the world (60-75% of my CPU to work with), and I see no reason for the problems I'm having.

Because it would be a massive run-on sentence to describe everything that's not working, I'll put it down as bullet points.

• Refuses to load heightmaps for no discernable reason (configuring two the same way, it will load one and not the other)
• Trying to create new map results in black void with absolutely no game objects, but unable to add more - They don't load
• Trying to open previously saved map results in same black void and same inability to add anything
• Saves over vanilla game data despite telling game to save in new map file
  
• Sometimes doesn't save at all, giving me this same black screen
• When it does save, physics objects fall through the world and disintegrate beneath the level
• Sometimes crashes outright when saving, opening, or making a new map file

I'm running on an fresh, unmodified install of the game, with all files verified to be 100% normal through both Steam and the built-in verification system. I'm at a loss of what to do, and disapointed that I can't make my own levels at the moment. I've googled this error, and it seems like some people have had it in the past, but there were no replies and they're all fairly old.

I've also attached my latest three crash logs. If anyone familiar with them can understand what the problem is (if the problem is evident from the log), I would love to know so I can hopefully fix it.