SeasonProvider.IsIgnored will properly handle a season that does not exist in the DB (TV DB doesn't have the latest season is root of the problem, or the season just started and NB DB is out of date).

NzbDrone.Core/Providers/SeasonProvider.cs

@@ -65,11 +65,12 @@ namespace NzbDrone.Core.Providers
 
         public bool IsIgnored(int seriesId, int seasonNumber)
         {
-            if (_sonicRepo.Single<Season>(s => s.SeriesId == seriesId && s.SeasonNumber == seasonNumber).Monitored)
-                return false;
+            var season = _sonicRepo.Single<Season>(s => s.SeriesId == seriesId && s.SeasonNumber == seasonNumber);
 
-            Logger.Debug("Season: {0} is not wanted for Series: {1}", seasonNumber, seriesId);
-            return true;
+            if (season == null)
+                return true;
+
+            return season.Monitored;
         }
 
         public void DeleteSeason(int seasonId)