Sync Metadata clears the Altitude field of all selected photos when just GPS (but not Altitude) is checked (incorrect). Pasting the clipboard into the GPS field also clears Altitude (incorrect). A metadata preset with just GPS checked also clears the Altitude field (incorrect).
The Altitude field shouldn't be modified when copying just GPS. This is clearly not designed behavior, since otherwise there would be no point in having a separate Altitude checkbox in the Sync Metadata and Metadata Preset dialogs. The bug was introduced somewhere between LR 6.14 and 9.1.
To reproduce on LR 13.2 / Mac OS 14.4.1:
1. Download and open this small catalog:
https://www.dropbox.com/scl/fi/fpom4b2bgdhmfdfxjlbhr/copy-gps-bug.2024.04.29.zip?rlkey=gssyo3jfgvpih...
2. Observe in the Metadata > Location panel that both photos have non-blank GPS and Location fields.
3. In Library Grid view, select both photos, with 1.jpg most selected.
4. Do Sync Metadata, click Check None, check just GPS (not Altitude), then click Synchronize. Observe that Altitude is now blank for both photos (wrong).
5. Exit LR, unzip a fresh copy of the catalog, and restart LR.
6. Observe that both photos have non-blank GPS and Location fields.
7. Select 1.jpg and copy its Metadata > Location > GPS field into the clipboard (Cmd C).
8. Select 2.jpg, click on its Metadata > Location > GPS field, and paste the clipboard (Cmd V). Observe that its Altitude field is now blank (wrong).
9. Exit LR, unzip a fresh copy of the catalog, and restart LR.
10. Observe that both photos have non-blank GPS and Location fields.
11. Select 1.jpg and in the Metadata panel, click Preset > Edit Presets.
12. Click Check None, check GPS (but not Altitude), do Preset > Save Current Settings As New Preset, and name the preset "GPS Only".
13. Select 2.jpg and do Metadata > Preset > GPS Only. Observe that Altitude is cleared (incorrect).