Should an aircraft registration match the flag next to it? More specifically, I have noticed that on several of the aircraft of Blue Panorama Airlines, even though they are an airline based in Italy and the Italian flag (together with the EU flag) were on each of the aircraft's tails, they all had an aircraft registration prefix of "EI", which is obviously the prefix for Ireland.  


Why do the flags and registration prefixes contradict?
Even if there is a reason for that, why does an Italian airline have aircraft registered in Ireland?
That's because the aircraft (some of them at least) are leased from Aerotron Ireland Ltd., an aircraft leasing company in Drogheda Ireland.   

I only looked up one. It was EI-FVA.
Here it shows it being registered to Aerotron on Aug 23, 2016.
And here it shows it entering Blue Panorama's fleet on Dec 8, 2016.