by haavid@falch.net:

What steps will reproduce the problem?
1. Create a new FileServer to serve from a directory containing an index.html file.
2. Load the directory "/" or file "/index.html" in a browser.
3. Make changes to index.html and reload it in the browser.

What is the expected output?
The new version of index.html.

What do you see instead?
The old version of index.html.

Which compiler are you using (5g, 6g, 8g, gccgo)?
6g

Which operating system are you using?
Linux x86_64

Which version are you using?  (run 'go version')
weekly.2012-03-22

Please provide any additional information below.
If you also add or remove files in the same directory as index.html, or similar
operations, the problem will not occur. The bug also depends on the browser having a
cached version, and sending a "If-Modified-Since" header in the request.
This is happening because checkLastModified() is being called a few lines too early in
serveFile(), causing it to check the modification time of the directory rather than the
index file.
Short fix has been submitted for review, but will wait until after Go 1.