I'm working with a designer friend on an iPhone app and he likes to refine all sorts of images relating to the project we're working on. All these images have been added to the project previously (and added to the project folder by xcode) and then are modified in their new location. When I preview the images in xCode, the updated images show up but building and running in the simulator or on a device doesn't pick up the new image. In fact, if I do a clean build it seems to ignore the image all together and blank spaces appear where images should be.

Now, I can delete these files from the project and re-add them and everything works peachy again. But there are a lot of them and I'd rather not do that every time an image is updated. Is there a way to get xCode to review and "learn" about these modified images? Is there a good reason for why it's not doing that automatically?