[reactive] mappend laziness issue

I started playing with reactive again and got stuck on a laziness issue with mappend. My codes pretty simple, two events controlled by legacy adapters, one and two. I'm combining them with mappend. both = one `mappend` two For some reason the events get clogged up. So for the first "one" event to fire, a "two" needs to come through, and sometimes vice-versa. It's possible I'm misunderstanding how mappend works, but the docs make it seem that both should fire whenever either fires. Thanks in advance.