Why is IE 7 renaming downloaded XLA files as XLS when saving?

Question

I have an Excel Add-In file I'm publishing on an intranet (plain ol' HTTP download, not an attachment in Sharepoint, etc.).

With IE 7, the user click the link and selects "Save", only to have the file renamed from "myaddin.xla" to "myaddin.xls". Firefox and Chrome work fine.

Since they are trying to overwrite an existing file in the Library folder and these are not sophisticated users, this issue is complicating my life.

Is there anything I can do on the server (MIME type change, etc.) to force IE7 to leave the extension as-is?

Answer 1

Its seems like a bug in Internet Explorer. One solution I think is to programatically rename the file back to .xls

But I still feel that the best option is to ask your user to use "Save as" instead and save it explicitly as ".xla". Everyone around seems to be doing this.

Answer 2

Have you had a look at this Microsoft KB article? Apparently, xla files are really xls files with no worksheets, and therefore have the same MIME type. You might try specifying an alternative MIME type to fool IE7 into leaving the extension alone.