I run the following test in one of my indexed folders:
I created a duplicate of a pdf file having the URL property set to a certain address
I moved the copy into the database, change URL property and then exported back to folder
New URL is correctly shown in DT file list pane (makingthe URL column visible) but the change is not transferred to the extended attribute of the filesystem (com.apple.metadata:kMDItemWhereFroms): i.e. if I check the file property in Finder (with Get Info) I still see the old URL
Pdf copy file is still shown as a duplicate of the original file even though it now differs in URL property
Running the same test on doc metadata results in correct passing over new properties to filesystem.
Is it an intentional behavior? To me it seems to be misleading.