ASP.NET Bundling – Bundle not updating after included file has changed (returns 304 not modified)

I just had the exact same problem. I have a folder with 2 CSS files:

• ~/Content/main.css
• ~/Content/main.min.css (pre-existing from my previous manual minification process)

My bundling code is this:

bundles.Add(new StyleBundle("~/css/main").Include("~/content/main.css"));

No matter how much I changed my main.css the output was the same url with the same contents:

<link href="https://stackoverflow.com/css/main?v=6Xf_QaUMSlzHbXralZP7Msq1EiLTd7g1vId6Vcy8NJM1" rel="stylesheet"/>

The only way to update the bundle was to rebuild my solution – obviously not the best approach.

However as soon as I deleted main.min.css, everything started to work just fine. Playing a little more I discovered that if there are both main.css and main.min.css, then updating main.min.css will actually update the bundle… Weirdness, but at least predictable.