First shot on fixing the sorting issue reported by many users.

The position of the album in the parent album is now preserved.
Updated RestKit to latest master & did some formatting

Classes/RKMTree.m

@@ -25,10 +25,10 @@
 
 #import "RKMTree.h"
 
-@interface RKMTree()
+@interface RKMTree ()
 
-- (NSArray*) sortEntitiesByRelativePosition;
-- (NSString*)getItemIDFromURL;
+- (NSArray *)sortEntitiesByRelativePosition;
+- (NSString *)getItemIDFromURL;
 
 @end
 
@@ -37,39 +37,60 @@ @implementation RKMTree
 @dynamic url;
 @dynamic rEntity;
 
-#pragma mark - 
-#pragma mark private
+////////////////////////////////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////////////////////////////////
+#pragma mark -
 
-- (NSArray*) sortEntitiesByRelativePosition {
-    NSSortDescriptor* descriptor1 = [NSSortDescriptor sortDescriptorWithKey:@"positionInAlbum" ascending:YES];
-    NSArray* entities = [[self.rEntity allObjects] sortedArrayUsingDescriptors:[NSArray arrayWithObjects:descriptor1, nil]];
-    return entities;
+- (RKMEntity *)root {
+	if ([self.rEntity count] > 0) {
+		NSArray *filtered =
+		        [[self sortEntitiesByRelativePosition]
+		         filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:
+		                                      @"(itemID == %@)", [self getItemIDFromURL]]];
+		RKMEntity *entity = [filtered objectAtIndex:0];
+		return entity;
+	}
+	else {
+		return nil;
+	}
 }
 
-- (NSString*)getItemIDFromURL {
-    NSArray *urlComponents = [self.url componentsSeparatedByString:@ "/"];
-    NSString *tmp = [urlComponents lastObject];
-    NSString * itemID = [tmp stringByReplacingOccurrencesOfString:@"?depth=1" withString:@""];
-    return itemID;
+
+- (NSArray *)children {
+	if ([self.rEntity count] > 1) {
+		NSArray *filtered =
+		        [[self sortEntitiesByRelativePosition]
+		         filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:
+		                                      @"(itemID != %@)", [self getItemIDFromURL]]];
+		return filtered;
+	}
+	else {
+		return nil;
+	}
 }
 
-- (RKMEntity*) root {
-    if ([self.rEntity count] > 0) {
-        NSArray *filtered = [[self sortEntitiesByRelativePosition] filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"(itemID == %@)", [self getItemIDFromURL]]];
-        RKMEntity* entity = [filtered objectAtIndex:0];
-        return entity;
-    } else {
-        return nil;
-    }
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////////////////////////////////
+#pragma mark -
+#pragma mark private
+
+- (NSArray *)sortEntitiesByRelativePosition {
+	NSSortDescriptor *descriptor =
+	        [NSSortDescriptor sortDescriptorWithKey:@"positionInAlbum" ascending:YES];
+	NSArray *entities =
+	        [[self.rEntity allObjects] sortedArrayUsingDescriptors:
+	         [NSArray arrayWithObjects:descriptor, nil]];
+	return entities;
 }
 
-- (NSArray*) children {
-    if ([self.rEntity count] > 1) {
-        NSArray *filtered = [[self sortEntitiesByRelativePosition] filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"(itemID != %@)", [self getItemIDFromURL]]];
-        return filtered;
-    } else {
-        return nil;
-    }
+
+- (NSString *)getItemIDFromURL {
+	NSArray *urlComponents = [self.url componentsSeparatedByString:@ "/"];
+	NSString *tmp = [urlComponents lastObject];
+	NSString *itemID = [tmp stringByReplacingOccurrencesOfString:@"?depth=1" withString:@""];
+	return itemID;
 }
 
+
 @end

Classes/RKObjectLoaderTTModel+fix.m

@@ -27,10 +27,13 @@
 
 // RestKit
 #import "RKMTree.h"
-#import "RKMItem.h"
+#import "RKMEntity.h"
 
 @implementation RKObjectLoaderTTModel (fix)
 
+////////////////////////////////////////////////////////////////////////////////////////////////////
+////////////////////////////////////////////////////////////////////////////////////////////////////
+#pragma mark -
 #pragma mark RKModelLoaderDelegate
 
 - (void)objectLoader:(RKObjectLoader *)loader willMapData:(inout id *)mappableData {
@@ -40,20 +43,54 @@ - (void)objectLoader:(RKObjectLoader *)loader willMapData:(inout id *)mappableDa
 			NSMutableArray *newEntity =
 			        [[NSMutableArray alloc] initWithCapacity:[origEntities count]];
 
-			NSDictionary *entity =
-			        [( (NSDictionary *)[origEntities objectAtIndex:0] ) objectForKey:
-			         @"entity"];
-			int i = [[entity objectForKey:@"id"] intValue];
+			int i = 0;
 			for (NSDictionary *origEntity in origEntities) {
 				NSMutableDictionary *oneEntity = [origEntity mutableCopy];
 
-				// inject the position in the array
 				NSMutableDictionary *entity =
 				        ([(NSDictionary *)[oneEntity objectForKey:@"entity"]
 				          mutableCopy]);
-				[entity setObject:[NSString stringWithFormat:@"%i",
-				                   i] forKey:@"positionInAlbum"];
 
+				/*
+				 * Each album is at a certain position within it's parent album.
+				 * If we just iterate over the album and enumerate the items the
+				 *position in
+				 * the parent album is lost.
+				 * For that reason the position index of the album (root) must be
+				 *preserved.
+				 */
+				if (i == 0) {
+					RKManagedObjectStore *store =
+					        [RKObjectManager sharedManager].objectStore;
+					NSString *predicateString = [entity objectForKey:@"id"];
+
+					NSFetchRequest *request = [RKMEntity fetchRequest];
+					NSPredicate *predicate =
+					        [NSPredicate predicateWithFormat:@
+					         "itemID = %@", predicateString, nil];
+					[request setPredicate:predicate];
+
+					NSError *error;
+					NSArray *objects =
+					        [[store managedObjectContext]
+					         executeFetchRequest:
+					         request       error:&error];
+					if ([objects count] > 0) {
+						RKMEntity *object =
+						        [objects objectAtIndex:0];
+
+						NSNumber *positionInAlbum =
+						        [NSNumber numberWithInt:
+						         [object.positionInAlbum intValue]];
+
+						[entity setObject:positionInAlbum forKey:
+						 @"positionInAlbum"];
+					}
+				}
+				else {
+					[entity setObject:[NSString stringWithFormat:@"%i",
+					                   i] forKey:@"positionInAlbum"];
+				}
 				[oneEntity removeObjectForKey:@"entity"];
 				[oneEntity setObject:entity forKey:@"entity"];