one-click-update (1.2.1 to 1.3) fails with the following message:
Archive is incomplete: some files are missing (eg. /index.php).
This is very unusual, so maybe you’re working on it right now, deleted some files and the updater can’t find the right ones?
From 0.x to 1.2.1 I’ve never had any problems one-click-updating to the new version. The servers normally seem very robust for handling Piwik…