For a long time now airlines got creative (eg. using the many loopholes provided by national, bi-lateral and EU tax regs and legislations). Employees are kind of riding the "bus" under the impression (were made beleive by magenta/orange/red/blue/"insert any other color here" presentations by their respective HR departments) that they have got a good deal by paying tax here, socal security there whilst being based elsewhere. These are the realities of flying for an outfit in Euroland these days I'm afraid. All is good and well until the taxman sends you a letter or worse comes knocking down your door.