IBook G4 and FreeBSD 9.0-RC2: unable to create four slices on hard drive?

[Torfinn Ingolfsen]

Today I made free space on the internal hard drive of my iBook G4.
Logical next step: install FreeBSD 9.0-RC2 on that free space. :-)

So I did. The installation went fine, with one small hitch: it seems like it is not possible to create a fourth partition
(or is i fifth? Anyway, ada0s4) on the internal drive. So currently there isn't a swap partition on the drive.
First I thought this was a problem with the bsd installer, but after FreeBSD is installed, gpart also has this problem:
kg-ibook# gpart show ada0
=>        5  117210235  ada0  APM  (55G)
          5     262203        - free -  (128M)
     262208   52626616     2  apple-hfs  (25G)
   52888824       1600     1  apple-boot  (800k)
   52890424   29358528     3  freebsd-ufs  (14G)
   82248952   34961288        - free -  (16G)

As you can see, the drive is APM partitioned, and there is 16 G of free space on it.
g-ibook# gpart add -s 2G -t freebsd-swap ada0
gpart: index '4': No space left on device

This make noe sense to me: I have created more than four partition on a APM partitoned drive before.
Any clue to what the problem is?

More details about this machine and FreeBSd on the FreeBSD page for it[1].

References:
1) http://sites.google.com/site/tingox/ibook_g4_freebsd

-- 
Torfinn