Hyperthreading on 32Bit but not on 64Bit?

Hyperthreading on 32Bit but not on 64Bit?

I have a strange situation.
2 computers with identical hardware, both Core i5, exactly the same model.
The only difference is the os, one has 12.04 32Bit the other one 12.04 64Bit.
The problem is that hyperthreading is only enabled on the 32Bit os and not
on the 64Bit os.
Can you tell me why and how I can enable it?
I looked in Bios and both have exactly the same settings, both
hyperthreading enabled in Bios but not in os.
2 logical processors:
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 2
On-line CPU(s) list: 0,1
Thread(s) per core: 1
Core(s) per socket: 2
Socket(s): 1
NUMA node(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 42
Stepping: 7
CPU MHz: 2294.665
BogoMIPS: 4589.73
Virtualization: VT-x
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 3072K
NUMA node0 CPU(s): 0,1
4 logical processors:
Architecture: i686
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 4
On-line CPU(s) list: 0-3
Thread(s) per core: 2
Core(s) per socket: 2
Socket(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 42
Stepping: 7
CPU MHz: 800.000
BogoMIPS: 4589.36
Virtualization: VT-x
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 3072K