There is one particular Excel file that is used by a number of employees at my company. It is edited from both Excel 2003 and 2007, with the "Sharing" feature turned on to allow multiple writers at once.

The file has a decent amount of data on several sheets with some basic formatting, and used to be about 6MB, which seems reasonable for its content. But after a few weeks of editing, the file grew to 10, then 20 MB, and eventually skyrocketed to more than 150 MB, even though it still has about the same amount of data as before. It now takes 5-10 minutes to open it, and that much time again to save it.

The first time this happened, I copied the content of each sheet into a new, blank workbook, and saved the new workbook; this brought it back down to about 6MB. Now, it has blown up again.

The workbook uses the "Data Validation" feature to limit the values in certain columns to the contents of a few named ranges. Copying all the data into a new workbook means re-setting up all the data validation, which is a pain and not something that we want to do every month.

As a troubleshooting step, I tried saving the file in "XML Spreadsheet 2003" format, hoping to get some insight into what was being stored. Sure enough, the file was almost a gig, and almost all of the 10 million lines look like this:

<NamedCell ss:Name="Z_21D5114F_E50C_46AC_AA4F_C3FF540C717F_.wvu.FilterData"/>
<NamedCell ss:Name="Z_1EE2BA5E_3011_4F9A_8ACD_E58835250FC4_.wvu.FilterData"/>
<NamedCell ss:Name="Z_1E3BDCEA_6A72_4ECC_BF4F_7B03CC66181E_.wvu.FilterData"/>

I've seen a few VBScripts online to manage and enumerate named cells that are hidden in Excel's built-in interface, though I wonder how they'd handle my 10 million named cells. What I really need, though, is an understanding of why this keeps happening. What actions in excel could be causing this?