Link Soucre changes when Spreadsheet opened from with within Outlook

When I send an Excel workbook as an attachment the source of the links
(links are to another excel sheet on a networked drive) defaults to
C:\ (but maintains the same network reference) when the sheet is
opened from within Outlook.

If the attachment is first saved and then opened the source remains
correct ie. The original network location of the linked file.

Does anyone know how to prevent this from happening?

Many thanks

Cy