wierd problems about systemmonitor's acpi temperature

[bruce]

dataEngine("systemmonitor").connectSource("acpi/Thermal_Zone/0/Temperature",plasmoid,500)

in my plasmoid i use the preceding statements to connect to 
"acpi/Thermal_Zone/0/Temperature", and use  plasmoid.dataUpdated to receive 
temperature data.

but there is a very wierd problem:
1, at the very beginning, it works at least for 10 days. i can receive cpu 
temperature data. i extract temperature data from data["value"]
2, but suddenly for unkown reason, i can not receive temperature anymore.
dataUpdated method is still be called periodly, but data["value"] is 
undefined. 
3, in someone else's machine, 
dataEngine("systemmonitor").connectSource("acpi/Thermal_Zone/0/Temperature",plasmoid,500) 
returns true, but dataUpdated is never be called!

here is my question:
1, from where  does systemmonitor dataengine 's datasource 
"acpi/Thermal_Zone/0/Temperature" retrieve temperature data?  is it from 
directory '/proc/acpi/thermal_zone'? or '/sys/class/thermal/thermal_zone0'?

2,  when wierd problem #2 happened, i checked directory 
'/proc/acpi/thermal_zone',and found its gone, but i am sure it really did 
exists for a long time. same machine, same operating system, why does this 
happens?

any information is welcomed, thanks advance!