Tethered capture does not apply custom metadata fields from metadata preset

In Lightroom Classic 11.5, photos taken in Tethered Capture with a
metadata preset selected do not have the custom metadata fields (from
plugins like Negative Lab Pro) as specified in the preset.

To reproduce:

1. Install a plugin with custom metadata fields
2. Create a metadata preset that sets some standard EXIF fields and
   also some custom fields. (The bug also occurs if no standard EXIF
   fields are included in the preset.)
3. Using Tethered Capture, take some photos with the newly-created
   metadata preset

Expected behavior:

Photo has all of the metadata fields set as per the preset, including
the standard EXIF fields and the custom plugin fields. The preset
name is selected in the metadata preset dropdown menu (the top item in
the Metadata Panel).

Actual behavior:

Photo has the standard EXIF metadata fields set as per the preset, but
all custom metadata fields are empty. The preset name is not present,
and instead "None" is selected in the dropdown menu.