Location Control

Standard System 3.5.2sp4

On a location controlled stock room, I have a
few part numbers that have 'somehow' ended with
negative balances in there locations (the total
of the locations still equals the balance of
the part, eg, my INP60 balance is 12, but my
location balances are 13 and -1)

I am trying to figure out how this has occured.
In file INPLF (location movements) I can see
entries that sets the locations to 13 and -1 but
how do I find out what program did this??
There is a Unique Reference # ,  what other files
is the ref # in, what does it reference to??
The Tran type is 'O' does this mean something??

Any pointers greatfully received.

Thanks,
Gary.