OpenGL ES (IPhone) alpha blending looks weird

I'm writing a game for IPhone in Opengl ES, and I'm experiencing a problem with alpha blending:

I'm using glBlendFunc(Gl.GL_SRC_ALPHA, Gl.GL_ONE_MINUS_SRC_ALPHA) to achieve alpha blending and trying to compose a scene with several "layers" so I can move them separately instead of having a static image. I created a preview in photoshop and then tried to achieve the same result in the iphone, but a black halo is shown when I blend a texture with semi-transparent regions.

I attached an image. In the left is the screenshot from the iphone, and in the right is what it looks like when I make the composition in photoshop. The image is composed by a gradient and a sand image with feathered edges.

Is this the expected behaviour? Is there any way I can avoid the dark borders?

Thanks.

EDIT: I'm uploading the portion of the png containing the sand. The complete png is 512x512 and has other images too.

I'm loading the image using the following code:

NSString *path = [NSString stringWithUTF8String:filePath];
NSData *texData = [[NSData alloc] initWithContentsOfFile:path];
UIImage *image = [[UIImage alloc] initWithData:texData];
if (image == nil) NSLog(@"ERROR LOADING TEXTURE IMAGE");

GLuint width = CGImageGetWidth(image.CGImage);
GLuint height = CGImageGetHeight(image.CGImage);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
void *imageData = malloc( height * width * 4 );
CGContextRef context = CGBitmapContextCreate( imageData, width, height, 8, 4 * width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big );
CGColorSpaceRelease( colorSpace );
CGContextClearRect( context, CGRectMake( 0, 0, width, height ) );
CGContextTranslateCTM( context, 0, height - height );
CGContextDrawImage( context, CGRectMake( 0, 0, width, height ), image.CGImage );

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData);

CGContextRelease(context);

free(imageData);
[image release];
[texData release];