I recently discovered that my Bluetooth mouse reports its battery level. I found out because it's reporting it as absolute axis data and every change in the reading is bumping the pointer all the way to the top left corner.

Here's a log of the input events:

$ input-events 7 -t 300
/dev/input/event7                       
   bustype : BUS_BLUETOOTH              
   vendor  : 0x3938                     
   product : 0x1001                     
   version : 258                        
   name    : "Interlink Bluetooth Mouse"
   phys    : "00:1C:26:E7:B4:4C"        
   uniq    : "00:12:A1:63:EF:3A"        
   bits ev : EV_SYN EV_KEY EV_REL EV_ABS EV_MSC

waiting for events
23:10:12.729503: EV_REL REL_X 16
23:10:12.729521: EV_REL REL_Y 2 
23:10:12.729528: EV_SYN code=0 value=0
...
23:10:38.041156: EV_ABS code=40 value=243
23:10:38.041176: EV_SYN code=0 value=0
23:10:44.116071: EV_ABS code=40 value=242
23:10:44.116092: EV_SYN code=0 value=0

The battery reports are the EV_ABS events, and code 40 is ABS_MISC. Every time this happens, the cursor jumps to 0,0.

I'm not sure whether these events are new to the latest Bluetooth code or if the older evdev driver just didn't react this way. But, this problem occurs on Ubuntu Karmic with the 2.2.2 release, and also with a fresh master branch build of everything.