I decided to start a new thread with this revelation from a prior discussion, because of its importance.
I have several iPad apps that apply metadata to raw images captured in the field using the camera connection kit. These apps have various export mechanisms, with a typical capability to bundle up raw images from the Photos app space with xmp files from the metadata editor app's space, and deliver them via ftp or however. I have seen failures where the creation date of the image file was made equal to the creation date of the xmp, and subsequent to export Bridge would not recognize the xmp file as valid edits to the raw file, even though they both had the same file name ahead of the extension. Up to now I never understood the cause of the failure. Opening the xmp file in a text editor and saving it out with a later creation date "fixed" the problem.
Adobe either needs to change this behavior (IMO the right solution, forget about checking creation dates) or at least publish the dependency. I believe there are a lot of programmers out there that had no idea that the creation date could invalidate the coupling between the raw file and the xmp file.