UA aircraft/seat change

I know this is a pretty piddly question but here goes. Have received notice from United that there is an aircraft change for our flight from IAD-FCO this fall (763 to 764). Our seats have been moved from regular economy to economy plus. Yes, I've flown EP before on overseas journeys & realize it's not much of an upgrade. Question is since we didn't pay the EP upgrade fare will they likely change us back to regular econ? Not a big deal really but never had this happen before!

I hope you get to keep your plus seating. It is very nice and because of the upgrade cost --on our way back from China a 14 hour trip-- no one from economy was allowed into the section without paying the fee so we had a whole row for almost every person in the section SWEET:D

Hope to keep the plus seating as well, would have no problem paying the small upgrade fee for the extra legroom but would be nice to get something complimentary from United for once!