When Arsenal were drawn against Rennes in the Europa League they were pulled out of the hat first and should be playing the second game away from home, so why aren’t they?

As we all know, there is a massive advantage in playing the second leg of a knock-out tie at home so why have Arsenal been giving a helping hand?
With both Arsenal and Chelsea playing in the Europa League, UEFA asked local authorities if both games could be played in the city on the same day for the last round. This wasn’t a problem with both Arsenal’s game against BATE and Chelsea’s game against Malmo being played in London on the same day, albeit with different kick-off times.
However, UEFA reportedly ‘insist’ that an ‘inversion’ is imposed during the knock-out phases if two clubs from the same city are expected to play on the same day and are not willing to let them go ahead in this round like they did the last.
The reason they switched Arsenal’s game and not Chelsea’s is that the Blues have ‘priority’ over Arsenal as they finished higher in the Premier League last season.
Their tie, in other words, gets to go ahead as originally drawn, while Arsenal’s has been switched even though that actually hands the Gunners an advantage!