Having a strange issue with Custom Properties and date type ranges.

Here is the setup: I have a named range in my spreadsheet with a date in it (example: 01-Jan-2011). This is formatted as a date dd-mmm-yyyy and I have not included any time information. Using the Advanced Properties, Custom tab I have "linked" to this Named Range field. Excel correctly picks this up as a date type.

Here is where the fun begins, I change my PC time-zone to Brussells, Paris, etc. save and close the spreadsheet. Now I change my time-zone back (in my case CST) open the spreadsheet and now the data in the date cell shows 12-31-2010 07:00:00 (wrong date, time information has been added, by system?).

I can toggle back and forth between time-zones and reproduce this problem time after time. If I remove the Custom Properties Link, the cell behaves as normal again, also this issue only seems to happen when moving in negative time zones (-6 as opposed to +6)

In my case this is impacting a SharePoint solution but the example above can be reproduced in Excel alone. I have several ideas for "work-arounds" but would like to understand what is going on before I pick one.

Can anyone help?