EU can of worms
The situation is very confused with no joined up thinking between EU states, unfortunately the cerably challenged EU rule makers can't get their walnut sized brains around the fact that some one can be employed by a company based in state A, live in state B and be based in state C.
This person will be largely using the system in the state they live but currently the EU rules say they should pay their social tax in the state they are " based" in, dispite the fact that they will never call on the social system in this state.
The state the company is registered in might well want the income tax.
So it is more than posable to pay social tax in one EU state, income tax in another EU state, and live in another EU state who won't have a call on any money from you because you have paid all your dues to the two other states.
This is a situation that will not please the EU state you are resident in, but it is amazing what seems to be a good idea when you work in the EU offices in Brussels.
No wonder UKIP is getting so popular in the UK.