Well, I'd seen this come up on a few newgroups/forums, and I thought about doing a write-up, and of course, someone else is smarter and quicker than me... but, I won't hold it against him.
RK Mcswain, on his blog, CAD Panacea reveals the mystery behind the workings of autosave. http://rkmcswain.blogspot.com/2005/07/autosave-mystery.html
And, as for my question the other day, about wacky blocks; between my readings on the autodesk knowledgebase, the help files and explanations from those more experienced/informed than myself (Mark H., Eric W., Richard L.), I've come to the firm realization that:
no, these anonymous blocks can't be edited by the normal commands (for the most part! as seeing a couple of them show up in the rename dialog but not the rest is what sent me on this crazy crusade)
yes, these blocks all seem to show up in qselect
sometimes these blocks will show up when you purge them, other times they won't (deleted the same blocks from duplicate drawings, one showed them in the purge dialog, others didn't, but, both were afterwards missing from the qselect list)
the prefixes (*E, *U, *X, etc), I'm informed, are for different types of entities. it's hard to clearly say which types. I was unable to explode a couple of them, and I'm collecting unexplodable blocks as a hobby to play with in my 'free' time. hahahahahahahaha
even more fun, I had some nested blocks (comes from copy, paste, bind, export to acad, flatten and any number of other things), some of which had anonymous blocks in them, some were anonymous blocks which just contained regular blocks within them.
so, it was just a matter of either properly exploding, or flat-out replacement of these blocks (I did a qselect of the blocks starting with asterisk u and copied them into another drawing and worked on them there for simplicity's sake).
oh, and when I was cleaning up these drawings (making sure the blocks were on '0' and bylayer then renaming them to things that make sense), I realized that when I was looking at the blocks in design center, then right-clicking to edit them, then I'd go back and I wasn't sure which ones I'd edited yet, because their previews weren't accurate any longer... I ran BLOCKICON, and viola'! the thumbnails were accurate.
I recently saw a lisp routine which changed a block's entities all to bylayer, but, I can't recall where I'd found it, so I'll have to do a search and post a link back when I think about it.
that's enough from me for now. happy cadding.