I released a new plugin to the .org repository about a month ago, and have committed several new versions since then, but the pie chart on the stats page has always stayed at 100% for an arbitrary version. For example, a week or so after 1.1 was released, it said that 100% of users had 1.0 installed, and recently it's been saying that 1.1.2 has 100%. I released 1.1.3 yesterday and it's gotten about 75 downloads so far, but the chart still says 1.1.2 has 100%.
I realize there's probably some caching going on, but there's obviously a problem. It has around 1000 total downloads spread out over 5 releases, and we know that users don't update very frequently, so the chart should show the numbers spread out more. I'm guessing the next time it updates it'll say that 1.1.3 has 100%, like it's done for previous versions.
Am I doing something wrong in my readme.txt or main PHP files? I've always had
Version: [current version number] in the main PHP file and
Stable tag: [current version number] in the readme.txt, and the readme.txt passes the validator.. You can browse through the different versions at http://plugins.svn.wordpress.org/basic-google-maps-placemarks/tags/.
Update: The File Header page in the codex has a specification, which can be helpful in debugging issues.
Update 2: Now it's stopped working again.
It might just take a couple releases with the fixed headers to work, though.. I finally fixed it; see my answer below.