Unlimited multiple values error

Problem/Motivation

Using Drupal 7 dev version, when unlimited multiple values are selected in the field settings, then the user can only add 2 phone numbers before it shows the following error when trying to add a third value:
"An illegal choice has been detected. Please contact the site administrator."

Proposed resolution

Right now, the only workaround is to stipulate the number of fields, and not use the unlimited option unless you only need two available.

Remaining tasks

A patch needs to be developed to fix the error.