The change of licence is in response to criticism of its wording from the Free Software Foundation ("too vague; some passages are too clever for their own good, and their meaning is not clear."), as well as issues raised during legal proceedings in the US.
The licence change will apply to future releases of pgAdmin III; both official versions and updates released with PostgreSQL installers. Existing users may, at their option, use older versions under the terms of the new licence.
If you have contributed to the pgAdmin III project in the past and have any questions or objections regarding the intended licence change, please contact me immediately at dpage (at) pgadmin (dot) org.