I just noticed that Emacs will trim a very big file before saving it. I opened a 4.6 GB file (not the best thing to do, but anyway) and after saving, the file was trimmed to around 375 MB. It didn't warn me about the file size, trimming or anything. I'm using Emacs 22.1.1 for Mac.
Is this default behavior (I definitely hope not) or a bug?