Lightmap + Directional Light = Draw call problem

I am having issues with lightmapping with a directional light and then using that light to get real time shadows of dynamic objects. But on turning shadows on from no shadows there is a huge increase in the number of drawcalls irrespective of the culling mask. Following are the scenarios. My light's culling mask is only a single layer that of dynamic object

1. Firstly i have turned of shadows and only have dynamic object in the scene then the number of drawcalls are 3.

2. Now i turn shadows on to hard shadows my drawcalls become 12.

3. After this when i make static objects appear in the scene then draw calls becomes 106.(None of the static objects are in the dynamic object's layer)

4. Now the worst part is when i make light's culling mask to nothing the draw calls changes to 76. the change is 30 which is much more than the contribution of dynamic object... Where am i going wrong? Help..