I have two Gmail accounts, one as @gmail.com, one under a different domain that is my primary account. Frequently, I have two tabs open in the browser, one for each. The gmail.com tab will spontaneously switch to the primary email, so that both tabs show the same thing, after what seems like some kind of timeout period of inactivity. This behavior started a few weeks ago and is very consistent; prior to that, I've had no trouble since Google introduced multiple email support.
How do I restore the previous behavior of keeping the same email in each tab?