Three Boys Music Corp. v. Michael Bolton
The court notes that 129 songs called "Love is a Wonderful Thing" have been registered with the Copyright Office. You can search the registration database online to get more details. You'll see that both Michael Bolton and the Isley Brothers have registered a work under that title.
As a side note, Jimi Hendrix began his music career as a back-up guitarist to the Isley Brothers in 1964.