Why does an Excel Recalc cause traffic over Network ?
 

Server: Windows Small Business Server 2003
Client: P4, 1Gb RAM, Win XP Pro, Office 2003

We have a 4Mb Spreadsheet that has HEAPS of vlookup formulas.
The vlookups refer to data in the same spreadsheet - there is no link
to any other spreadsheet.
If I do a RECALC(F9) on a client it takes about 7 Seconds and I notice
the LED on the network card flashes heaps - indicating traffic.
If I save the spreadsheet to the hard drive of the client, open it and
recalc I get the same behaviour BUT if I disconnect the client from the
network (Unplug the cable or remove from the domain) the recalc only
takes 1 second !!??.
Why is the recalc sending traffic over the network - shouldn't all the
processing be done at the client itself ?