ASP.NET/ IE / Excel interaction ([1] appended to the file name)

Hello,

I'm streaming an Excel file to IE using the content-disposition header. If
the user opens the file, Excel appends a "[1]" to its name (the name looks
file in IE temporary internet files). It causes a problem as the source for
the pivot table is not recognized (the file is created by using Reporting
Services and finalized by using Aspose.Cells).

If the file is saved (even under another name) and then opened, it works
fine...

At which level is this extra [1] handled ? Is this possible to workaround
this problem ?

TIA