Bug 434594

SUMMARY
With digikam configured to write metadata to sidecar files only,
add caption to jpeg, copy jpeg file but not sidecar (outside digikam). New
file has caption.

STEPS TO REPRODUCE
1. Configure digikam as follows:
Settings->Configure->metadata->Behaviour
.Write to metadata
..Image tags
..Captions and title
..Timestamps
..Geolocation info
.Reading and writing metadata
..Update file modification
..Rescan when files modified
Settings->Configure->metadata->Sidecars 
.Read from sidecar files
.Write to sidecar files
.Write to XMP sidecar only
.Sidecar file names are compatible with commercial programs

2. Outside digikam, create new jpeg (screen capture) and save to existing
album folder
3. Use exiftool to check nothing odd in the jpeg file
4. In digikam change caption (creates sidecar file)
5. Use exiftool to verify jpeg file has not been changed
6. Outside digikam, copy jpeg file - but not xmp file - to new name in
same folder
7. digikam finds new image but shows caption same as the original,
even though there is no matching sidecar file
8. Use exiftool to verify that no caption has been written to either
jpeg file

OBSERVED RESULT
Digikam shows same caption for new file as old file, even though it
doesn't have a sidecar file or embedded caption.

EXPECTED RESULT
Empty caption.

SOFTWARE/OS VERSIONS
Windows: 10

ADDITIONAL INFORMATION
I'm not sure if this should be higher priority. While I appreciate that
it's a contrived situation, it's putting me off making a complete switch
to digikam until I understand why this has happened and whether it can
happen under other image-importing situation.