I tested now and these are the results:
`
exiftool -G -s -a -m -u -args Living\ Room.jpg | grep "This is the caption"
-File:Comment=This is the caption text.
-EXIF:ImageDescription=This is the caption text.
-EXIF:UserComment=This is the caption text.
-XMP

escription=This is the caption text.
-XMP:ImageDescription=This is the caption text.
-XMP:UserComment=This is the caption text.
-IPTC:Caption-Abstract=This is the caption text.
exiftool -G -s -a -m -u -args Living\ Room.jpg | grep "This is the title"
-XMP:Title=This is the title.
-IPTC:ObjectName=This is the title.
exiv2 -pa Living\ Room.jpg | grep "This is the title"
Iptc.Application2.ObjectName String 18 This is the title.
Xmp.dc.title LangAlt 1 lang="x-default" This is the title.
exiv2 -pa Living\ Room.jpg | grep "This is the caption"
Exif.Image.ImageDescription Ascii 26 This is the caption text.
Exif.Photo.UserComment Undefined 33 This is the caption text.
Iptc.Application2.Caption String 25 This is the caption text.
Xmp.dc.description LangAlt 1 lang="x-default" This is the caption text.
Xmp.tiff.ImageDescription LangAlt 1 lang="x-default" This is the caption text.
Xmp.exif.UserComment LangAlt 1 lang="x-default" This is the caption text.
`
It seems that the workaround to avoid the incorrect title is to disable the Exif ImageDescription field, then ZenPhoto should use the IPTC ObjectName field, or the XMP Title field.
By the way, that ZenPhoto metadata documentation page does not list Exif as a source for "Zenphoto title", so either that documentation page is incomplete, or ZenPhoto is incorrectly using the IPTC:Caption-Abstract field for the title.