.DS_Store files are folder specific. Each folder gets one, and they are used for that folder no matter which user is logged in. A problem in a .DS_Store file would persist for any user, so it's not impossible that's the problem.
If so, is there a reasonable fix for this? (By which I mean, as usual, one that I might be able to implement with buggering up my machine and without having a nervous breakdown.)
I might add that folders I brought over from my old system don't share this bizarre behavior; ie, newly created documents placed inside do not snap to upper left corner upon being taken out for the first time.
The same seems to hold true for folders created on the new iMAC which have been around for a couple weeks (which makes the problem even more interesting ~ complex).
