The IAU website has this draft definition of "planet" and "plutons" page, published on 16 August 2006 in Prague. It says (emphasis mine):
The world's astronomers, under the auspices of the International
Astronomical Union (IAU), have concluded two years of work defining
the difference between "planets" and the smaller "solar system bodies"
such as comets and asteroids. If the definition is approved by the
astronomers gathered 14-25 August 2006 at the IAU General Assembly in
Prague, our Solar System will include 12 planets, with more to come:
eight classical planets that dominate the system, three planets in a
new and growing category of "plutons" - Pluto-like objects - and
Ceres. Pluto remains a planet and is the prototype for the new
category of "plutons."
The proposed 12 planets Solar System looked like this (credit: The International Astronomical Union/Martin Kornmesser):
The final press release, published on 24 August 2006, says:
The IAU members gathered at the 2006 General Assembly agreed that a
"planet" is defined as a celestial body that (a) is in orbit around
the Sun, (b) has sufficient mass for its self-gravity to overcome
rigid body forces so that it assumes a hydrostatic equilibrium (nearly
round) shape, and (c) has cleared the neighbourhood around its orbit.
This means that the Solar System consists of eight "planets" Mercury,
Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A new
distinct class of objects called "dwarf planets" was also decided. It
was agreed that "planets" and "dwarf planets" are two distinct classes
of objects. The first members of the "dwarf planet" category are
Ceres, Pluto and 2003 UB313 (temporary name).
Which looked like this (credit: The International Astronomical Union/Martin Kornmesser):
So in 8 days, the IAU switched from a 12 planets system, with a planet subcategory called "plutons", to a 8 planets system, with an dwarf planet category distinct from the planet category. How did that happen? It's probably something only a General Assembly attendant who witnessed the discussion would know. It must have been quite a debate!