I'm a fairly infrequent flyer who's a United MP (no status) member but has never had a CO FF account. About 2 weeks ago I purchased a round-trip economy itinerary at United.com for a Continental flight next weeked. The trip was only 3 weeks away and the only available seats on 3 of the 4 legs were middles. I checked back every day at UA.com until a couple days ago when my seat assignments and the plane maps for my itinerary suddenly disappeared. I was provided a link to the CO website where I was able to plug-in my confirmation number and I was given the choice of all the economy seats on the plane, including those with extra legroom. So I selected 4 such seats and was not prompted or alerted that they normally cost extra (nor do I think I was charged). And sure enough, my new assignments show up fine on both the CO & UA websites. When I click the seat change button on the UA site my assignment is shown but the only other available seats are the lousy regular middle seats that were around when I booked. Now a few days later I checked the CO site again just for kicks and while my seat assignments still look good, if I try to switch to another extra legroom seat I'm told it will cost extra.

I'm pretty sure it was just some temporary glitch that allowed me to get these seats. Do I have to worry about either losing my seat assignment or being forced to pay extra for them at some point?