THis sort of thing will continue until the tax situation is harmonized across Europe, I have no doubt pilots on contracts are paying there tax in Ireland, the problem is that each EU state has different rules and the local tax authority's want to enforce these local rules.
There should be no double taxation inside the EU but some of the authority's are very strict about the interpretation of residency the Danish are especially vigorous about this, I know of one Danish pilot who has property in Denmark but lives and pays tax in another EU state who was presented with a tax demand from the Danish authority's for tax as if he was resident in Denmark, if this demand had not been quashed his total tax burden across the two EU states would have been 120% of his income !
What is needed is a united front from the all the EU tax authorities towards people within aviation who work across the EU, all we have at the moment is some half hearted social tax legislation centered on the crewmenbers nominal base and NOT their state of residence.