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Epson printers will perform a random "maintenance and operation check" based on a formula that measures print volume and time since last used. I've looked for the details of that formula with no luck. It's not published and probably proprietary.
So, if the printer has been not used for a certain time (whether left on or off), it may go through the cycle before printing. Prior print volume, or perhaps current ink levels, appear to be part of the formula. Some users claim that the check cycle happens more frequently as ink levels get low.
The only way I know to anticipate the event is to do a nozzle check. If the printer is truly "ready", the nozzle check happens fast and uses very little ink. If the printer is not ready, it will do the long check cycle, then the nozzle check, then be ready.
And FYI, you would be better off taking your printing questions to the "Printers & Printing" forum at dpReview (http://forums.dpreview.com/forums/1003). There is much more activity and participation by knowledgeable users there than on Miranda and other forums.