I think what is happening is that Delta doesn't know whether it will be one of the 767-300ERs with the second door and one overwing exit (ex-Gulf Air or the one made for Continental) or one of the regular ones.

So what they are doing now, they're blocking row 21 and only allowing reservation of row 20. For example, looking at DL14 ATL-FRA for today (using http://www.benedelman.org/travel/dlseats/ ), both rows 20 and 21 are exits, and row 20 will not recline. Looking at tomorrow's DL14, row 21 is showing assigned, but not as an exit row, so I am guessing it's blocked until they determine which 767-300ER version it is.

In the past, they used to just block both rows 20 and 21 so this wasn't an issue.

Of course, what actually happens on the day of departure when a 2 overwing exit plane is assigned (and there are many many more of these), is anybody's guess.

Is this consistent with what everyone else is seeing?