I have excel files that I and several others in my group maintain
using macros from an add-in file that are located on the network
drive. We run the macros using form buttons that have the macros
assigned to them. For example, one button might be assigned to N:/
Budgets/BudgetMacros.xla!ClearCells. The reason that this add-in is
on the network drive is that it allows me to make changes without
having to re-distribute the file every time.

The problem is, when we email the file to a client (clients do not use
the macros) and get it back from the client, the button assignment has
changed to reference the C: drive instead of the network drive.
Example above: C:/Budgets/BudgetMacros.xla!ClearCells (which, of
course, does not exist).

We've experimented here in the office, and the it seems that just
opening the file from an email causes the change to happen (even if
the person opening the email has the add-in loaded).

Any thoughts on how to prevent this from happening, or how to overcome
it in a way that is not overly cumbersome? (Right now, we have to
remove the old buttons, and copy & paste new ones in from a file that
has correct assignments.)

Thanks in advance for any suggestions.