I've been looking for an answer to this for quite a while myself. It
doesn't even seem to matter if it was created by someone else or not;
charts seem to readjust themselves on their own whim whether or not
they were created by myself or someone else. And even charts that
worked fine one day, can change the next.
Do you get any messages when you activate and edit the chart -- like "edit
existing or convert all"?
What gets messed up with the chart when you edit it? You said the formatting
gets messed up -- but what does that mean, exactly? Colors? Fonts? Axis
scale? Something else?