because you don't configured it? Dou you mean with mouse control module yast2 
mouse? 
  
could you please provide hwinfo --mouse and /var/log/YaST2/y2log  

Its a laptop with a touchpad and a ps/2 connector (with no mouse attached). I
also plugged in the usb mouse.
I attached the yast2 log
hwinfo returns:

14: USB 00.0: 10503 USB Mouse
  [Created at usb.122]
  UDI:
/org/freedesktop/Hal/devices/usb_device_46d_c501_noserial_if0_logicaldev_input
  Unique ID: FKGF.rz1_gqIFXc9
  Parent ID: pBe4.aDK4e2xT5QF
  SysFS ID: /devices/pci0000:00/0000:00:1d.1/usb2/2-1/2-1:1.0
  SysFS BusID: 2-1:1.0
  Hardware Class: mouse
  Model: "Logitech Cordless Mouse Receiver"
  Hotplug: USB
  Vendor: usb 0x046d "Logitech Inc."
  Device: usb 0xc501 "Cordless Mouse Receiver"
  Revision: "9.10"
  Compatible to: int 0x0210 0x0015
  Driver: "usbhid"
  Device File: /dev/input/mice (/dev/input/mouse2)
  Device Files: /dev/input/mice, /dev/input/mouse2, /dev/input/event4
  Device Number: char 13:63 (char 13:34)
  Speed: 1.5 Mbps
  Module Alias: "usb:v046DpC501d0910dc00dsc00dp00ic03isc01ip02"
  Driver Info #0:
    Buttons: 5
    Wheels: 1
    XFree86 Protocol: explorerps/2
    GPM Protocol: exps2
  Config Status: cfg=new, avail=yes, need=no, active=unknown
  Attached to: #13 (Hub)

17: PS/2 00.0: 10500 PS/2 Mouse
  [Created at input.157]
  UDI: /org/freedesktop/Hal/devices/computer_i8042_Aux_3_Port_logicaldev_input
  Unique ID: AH6Q.845qvaQafo3
  Hardware Class: mouse
  Model: "SynPS/2 Synaptics TouchPad"
  Vendor: int 0x0212
  Device: int 0x0001 "SynPS/2 Synaptics TouchPad"
  Compatible to: int 0x0210 0x0003
  Device File: /dev/input/mice (/dev/input/mouse0)
  Device Files: /dev/input/mice, /dev/input/mouse0, /dev/input/event2
  Device Number: char 13:63 (char 13:32)
  Driver Info #0:
    Buttons: 3
    Wheels: 0
    XFree86 Protocol: explorerps/2
    GPM Protocol: exps2
  Config Status: cfg=no, avail=yes, need=no, active=unknown

18: PS/2 00.0: 10500 PS/2 Mouse
  [Created at input.157]
  Unique ID: AH6Q.RgweIoOI2K6
  Hardware Class: mouse
  Model: "PS/2 Generic Mouse"
  Vendor: int 0x0210
  Device: int 0x0003 "PS/2 Generic Mouse"
  Device File: /dev/input/mice (/dev/input/mouse1)
  Device Files: /dev/input/mice, /dev/input/mouse1, /dev/input/event3
  Device Number: char 13:63 (char 13:33)
  Driver Info #0:
    Buttons: 3
    Wheels: 0
    XFree86 Protocol: explorerps/2
    GPM Protocol: exps2
  Config Status: cfg=new, avail=yes, need=no, active=unknown

Actually, there is no y2log attached here...

This is now the second time that this happens, and I figured out why.
When I post a comment to a bug, I´m sometimes transferred by bugzilla to another
bug (which is completely unrealted to the one I posted the comment to). So I
posted "i attached the log", then I clicked on "post attachment" and so I
attached the logs to a different bug. Please tell this the webmaster so they
could fix this.
I´ll attach the logs immediately (this time to the right bug *g)

Created attachment 51237 [details]
YaST2 logs

all standard mice are combined to one mouse by the kernel input interface 
This behavior cannot be changed and is by the way a real cool feature because 
you don't need to do anything just plugin the mouse ;) 

Ok, I understood.
The problem for me was that YaST detected the touchpad and the external
connector. Since there was no mouse attached it didn´t enable the mouse wheel.
Wouldn´t this be better to have /dev/mice configured in X as a 5 button mouse
(with wheel) by default since the user could plug a mouse in at any time which
has a wheel. If there is no wheel mouse the kernel just doesn´t send the wheel
events.

What do you think of the above suggestion? If X configures the /dev/input mouse without a wheel I can´t just plug in an USB mouse and use all its functionality.

I changed the wheel default value in lib/hw/mouse.c to always provide
a wheel even if the currently connected mouse doesn't have a
wheel.

Cool. What about also changing the number of buttons to 5 so that all buttons of the attached mice work (IMHO there aren´t many mice which have more then 5 buttons, but it could also be set higher)?

Do you think this could be changed as well?

5 Buttons are always mapped in X no need to specify that explicitely