I have a task with the date specified as "every 1 month starting 25 Jan 2013". It is apparently next due on 27 March which doesn't seem right at all.
Unfortunately, the "every month" formula always treats a month as "30 days". We're sorry for the inconvenience, we'll correct this issue in the future.
For now, if you want to set a task that will repeat on the same day of every month, please try to set the task to "every 25" (or "ev 25").