planetpenguin-racer-extras does not have planetpenguin-racer as a dependency

The package planetpenguin-racer-extras should have the package planetpenguin-racer as a dependency. How can a user install extras for a game that is not installed?

Package: planetpenguin-racer-extras
Priority: optional
Section: universe/games
Installed-Size: 55096
Maintainer: Debian Games Team <email address hidden>
Architecture: all
Source: tuxracer-extras
Version: 0.5-3
Recommends: planetpenguin-racer (>= 0.3.1-1)
Filename: pool/universe/t/tuxracer-extras/planetpenguin-racer-extras_0.5-3_all.deb
Size: 14316986
MD5sum: 3b76192dbd1ca51a86b59f037536bc9c
SHA1: 89e0241f971985ef4cb09ff73014cbea5f88ddff
SHA256: acbf75133e9586e934fc27f8be736728935f7cfba75d681ca4bba922fb328b0b
Description: Additional courses for PlanetPenguin Racer
 This package contains over fourty extra courses for the game PlanetPenguin
 Racer.
 .
 If you install this package, startup time of "ppracer" might lengthen a bit
 (mainly depending on your harddisc speed). But I'm sure you will find it
 worth to wait a bit longer ;)
 .
  Homepage: http://tuxracer.fubaby.com/courses.php
Enhances: planetpenguin-racer
Bugs: mailto:<email address hidden>
Origin: Ubuntu

Package: planetpenguin-racer
Priority: optional
Section: universe/games
Installed-Size: 752
Maintainer: Ubuntu MOTU Developers <email address hidden>
Original-Maintainer: Debian Games Team <email address hidden>
Architecture: i386
Source: ppracer
Version: 0.3.1-10
Replaces: planetpenguin-racer-data (<= 0.3.1-6)
Depends: libc6 (>= 2.6-1), libfreetype6 (>= 2.3.5), libgcc1 (>= 1:4.2-20070516), libgl1-mesa-glx | libgl1, libglu1-mesa | libglu1, libice6 (>= 1:1.0.0), libpng12-0 (>= 1.2.13-4), libsdl-mixer1.2 (>= 1.2.6), libsdl1.2debian (>= 1.2.10-1), libsm6, libstdc++6 (>= 4.2-20070516), libx11-6, libxext6, libxi6, libxmu6, libxt6, tcl8.4 (>= 8.4.5), zlib1g (>= 1:1.2.3.3.dfsg-1), planetpenguin-racer-data (>= 0.3.1-10)
Recommends: planetpenguin-racer-extras
Conflicts: planetpenguin-racer-data (<= 0.3.1-6)
Filename: pool/universe/p/ppracer/planetpenguin-racer_0.3.1-10_i386.deb
Size: 278462
MD5sum: 2dcdd9a47546e9e5c81449e5b75f125b
SHA1: 5ed27aad8c352c3b668a7d1a7db2027339858766
SHA256: b1cfc2082fdd9c2105ff6354e91e54f2ea131489cb1b6088d851cec5782cc3b9
Description: another 3D racing game featuring Tux, the Linux penguin
 PlanetPenguin Racer, or ppracer as it is called for short, is a simple OpenGL
 racing game featuring Tux, the Linux mascot. The goal of the game is to slide
 down a snow- and ice-covered mountain as quickly as possible, avoiding the
 trees and rocks that will slow you down.
 .
 Collect herrings and other goodies while sliding down the hill, but avoid fish
 bones.
 .
 This game is based on the GPL version of the famous game TuxRacer.
 .
 You should have working 3D acceleration for your X or this game will run quite
 slow.
 .
  Homepage: http://projects.planetpenguin.de/racer/
Bugs: mailto:<email address hidden>
Origin: Ubuntu