Fixed: Now the UI will update properly if you change a custom quality title in the Quality table.

src/NzbDrone.Api/Qualities/QualityDefinitionModule.cs

@@ -27,7 +27,7 @@ namespace NzbDrone.Api.Qualities
 
         private QualityDefinitionResource GetById(int id)
         {
-            return _qualityDefinitionService.Get((Quality)id).InjectTo<QualityDefinitionResource>();
+            return _qualityDefinitionService.GetById(id).InjectTo<QualityDefinitionResource>();
         }
 
         private List<QualityDefinitionResource> GetAll()

src/NzbDrone.Core/Qualities/QualityDefinitionService.cs

@@ -12,6 +12,7 @@ namespace NzbDrone.Core.Qualities
     {
         void Update(QualityDefinition qualityDefinition);
         List<QualityDefinition> All();
+        QualityDefinition GetById(Int32 id);
         QualityDefinition Get(Quality quality);
     }
 
@@ -45,6 +46,11 @@ namespace NzbDrone.Core.Qualities
             return GetAll().Values.ToList();
         }
 
+        public QualityDefinition GetById(Int32 id)
+        {
+            return GetAll().Values.Single(v => v.Id == id);
+        }
+        
         public QualityDefinition Get(Quality quality)
         {
             if (quality == Quality.Unknown)