The screenshot is fine and you are right, it appears the file gets truncated when it's written. I've created a ticket for this bug: https://github.com/LambdaHack/LambdaHack/issues/302. It also contains a possible workaround. Please let me know if the workaround works for you and any feedback about the actual game (assuming it works fine this time, let's hope).
BTW, did you use a windows installer or the zipped binary to install the game? Unlikely, but potentially one of them may be failing in this way and another may be fine.
Reading the rest of you post, man, you are poet! :)