web.config - "This file has been modified outside the source editor" after every build?

I have inherited an asp.net-mvc3 project and the webconfig in the project folder is getting modified (set to a default/fixed set of config items) on every build. I thought that was due to conditional xslt config transforms but it's not. It doesn't matter what I have in the transformed web.debug.config as it doesn't overwrite what is generated in the webconfig.

Every time I modify the webconfig I get the dialog nag that "this file as been modifed outside the source editor" after each build.

Could this be in custom build settings? I'm totally at a loss here.

Solution

Do you have any Post or Pre build events in your properties:

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