Wierd exclamation point message when round tripping back from Photoshop?

Question

I have been using Photoshop CS3 for sharpening and other edits and have been hitting save (or just using a sharpening automation thing which saves the photo automatically) and I find that when I look at the new image in Lightroom it has an exclamation point, which when clicked says something like: "The metadata for this photo has been changed by another application. What would you like to do?" The options are "use disk metadata" "do nothing" or "overwrite" (I'm paraphrasing here).
First, does anyone know why I am getting this message? Second, what should I do when I get it? I've been selecting "overwrite" but I have no idea, really, what this whole dialog is about! Third, is there any way to NOT get this message?
Many thanks for your help!

Answer 1

Use Lr's help facility; it contains this entry:
Update photos changed by another application
In the Grid view, Lightroom displays alerts in image cells when the photos in your library have been changed by another application. For example, if a photo has a one star rating in Lightroom, and the photo has been updated to a two star rating in another application, you need to decide which rating to respect. Both cannot co-exist together. Lightroom lets you resolve conflicting photo metadata by either overwriting its data in the library with metadata from the photo or its sidecar XMP file, or overwriting the metadata in the photo file or sidecar XMP file with its stored data in the library database.
1. In the Grid view, double-click the alert icon in a cell.
2. In the Confirm dialog box, click one of the following:
Import Settings From Disk Imports the metadata from the photo or its sidecar XMP file, which overwrites the photos data in the library database.
Overwrite Settings Exports metadata from the library database to the photo file and overwrites the data in the photo or its sidecar XMP file.
Do Nothing Takes no action. If you select this option, be sure that the photos metadata in the library database doesnt conflict with data in the photo or its sidecar XMP file.