ExcelBanter - Sheet Names Randomly Change (Chart Sheets Only)

I have an Excel 2007 macro-enabled worksheet that is used as a template for
our entire department. It, and files made from it, are on a share drive.
Multiple people will access and make updates in each resulting file. We
cannot figure out when or why, but the tabs for charts will at some point,
ALL change names, from "xxxx plot" to "Chart6" or something like that (always
Chart plus a number). There are about 2 dozen total tabs, eight of those are
charts, and the digits in the new names aren't even consistent across files.
This is messing up a couple macros because the sheet being referred to no
longer exists with its original name. Also, it simply makes it harder to
find our plots.

Non-chart sheets never get renamed, but all the chart sheets seem to change
all at once. When you open up the file, you cannot tell if it had already
changed previously, or if the change occurred as you were opening the file.
No one has seen the change while they were in the middle of working on the
file. Not all files, which are actively being worked in (daily) for about 5
months, will change (maybe half have this happen).

Anyone know why this may be happening, and how to prevent it? I do not want
to totally lock down the charts, as people sometimes need to add text boxes
to explain info on the plots.

Thanks.