How much Levemir are you taking? the amount of time a basal insulin lasts depends, quite a lot, on how high the dose is.
Your basal may have passed its peak, but there may be a tail end still working, which keeps your blood glucose steady. I think the amount of time it lasts is different for different people, and maybe it just works longer for you.
You have to feel happy with the insulin you are using, and if you aren't it's better to try and find something that works better for you, but maybe that's why.