If I get that 'garbage' error, and refresh (resend the posted data as well) it goes to the post, if I try to edit it from there it doesn't work. This seems to happen most frequently when I'm in the editor for a lengthy period of time on a post, also. I'm not sure what's triggering it, usually it's when I'm highlighting text for deletion but I'll occasionally lose the cursor in the edit window. Every time the garbage error occurs it's a little different, it's like the beginning of the transfer was interupted locally (on the server). Almost like there was some new software installed that's causing some kind of interupt activity that's making the post routine hiccup.
Based on the mostly random nature of the error I'd say it's some sort of interrupt conflict, like different software using a shared global variable under certain circumstances.