Join Date: Aug 2011
Location: Barcelona, London, on a plane
Programs: IB+ Gold, TK E+, Hyatt Globalist, Marriott LTP, IHG Diamond
Posts: 14,182
It might be a minor glitch.
Group 1 is supposed to be those with the extra space seats at the front who have also paid for overhead bin space. Perhaps you managed to get one of the premium seats through luck and then the Vueling system gives you Group 1 to ensure that you find overhead bin space.
The IB+ codeshares are supposed to come with checked bag + overhead bin bag + underseat bag but Group 2 boarding. IIRC But to be honest it's been awhile since I booked VY as an IB codeshare since the value isn't there for me...