Whenever there's a windy day, our front door blows open (letting the weather in and the animals out) unless we throw the deadbolt. It's not a big deal when we're all inside - it's become second nature to throw the bolt just in case every time I come inside, whether it's windy or not - but it's a major pain to have to take my keys with me, and bolt the door behind me, whenever I step outside.
I suspect that the problem is just that the bolt of the regular lock doesn't extend quite far enough, but I don't know what I can do to change that. I thought of adding a shim or two behind the strikeplate in the doorjamb, but it's already scraping the door as it is.
I'm posting from work and didn't think to take pictures at home, but: the doorknob and deadbolt are keyed-alike, Schlage (I believe) and about 15 years old.