I generally leave JIRA/Confluence/Bamboo open in their own tab, and they restore when I reopen my browser.

However, I also use autocomplete for username, so it populates user field upon reopening browser.

If I do not login and leave the tab - and close the browser - I am presented with multiple "Are you sure you want to leave this page?" messages.

Simply having username or password entered on a login screen should not cause this popup...