Password Vault used to lock whenever you reloaded the page or left it, even for a moment. Now a tab that you have unlocked stays unlocked until the vault has gone unused for the time you choose, you click Lock, or you sign out.
Choose the time at the top of the Password Vault list: 5, 15 or 30 minutes, or 1 hour. It is 15 minutes unless you change it. A new browser tab still starts locked.
To do this, the tab keeps an encrypted copy of its key, and Magpie holds the key to that copy only until the vault locks. Magpie never has both, so it still cannot open your vault. The site's security policy was also tightened so that only Magpie's own scripts can run on its pages.