I still have some of my birds laying too! They aren't fertile though as they have been molting and about to finish up their molt, and yes, they laid during their molt.
I haven't tried to stop their egg laying, I really wouldn't know how to stop them from laying, besides putting them in a completely dark area? maybe?
I've had some melanistic hens lay everyday for a year. They didn't lay the next year or any time after that...I guess they ran out of their allotted number of ovums.
I have noticed in the past few years it's becoming more frequently a norm than a rarity. I really don't know what's causing the change in their reproductive systems but something is occurring to change their natural reproductive behavior, (weather, feed, or ?) I just don't know.
I really don't worry too much about it, when they quit laying they go to freezer camp. At the moment, I have 5 melanistic hens that have not layed an egg this year at all. Last year they laid the whole year, non-stop! They are all in different pens, so I don't think it's a 'female hormonal' thing happening.
Sorry I can't give you a better answer!