ev 111 days starting 24/05/2012
after first click on checkbox--> 1/1/2013
thank you for your report, I've been able to reproduce this issue and have passed it to the developers.
We've identified the issue. It turns out it's not a bug. The reason why the date is changed to January 1st in this case is because May 24th + 111 days = September 12th and this would be an overdue date. If a task is overdue, completing it will change the date to the next occurrence that isn't overdue (to avoid multiple checking off overdue tasks) and therefore May 24th + 222 days = January 1st.
Thank you !