When I request the total reaction force on the base of a Surface Spring Support, the result is unbalanced. There are 25.000N missing in this particular case.
it seems not a bug, there’s no boundary support and dof’s restrained at node of spring element. Probably, reaction force is available when using two node spring element.
in such condition CalculiX provide *Section print feature to get output force of surface set, unfortunately is not yet implemented in PrePoMax. So, user required to define manually in Edit CalculiX Keywords.
*edited
below simple test, results shown model of surface spring is in equilibrium.
Ok.Spring Surface is in balance but RFz of that surface is not available and deliver an empty value. Is that right?
My 75.000 N corresponds only to the nodes with BC z=0. 
indeed, there’s no reaction force output for unrestrained nodes.
So I see that the *Section print has some nice usages.
right, it can be useful to check free-body diagram of complex models. CalculiX will compute internal forces by integration, user only need to partition the model to defining surfaces of solid part.
Indeed, here’s an old discussion about it: Section print in history outputs
Since this is not really a PrePoMax bug I will close the topic.