It watches for the file to be modified, once it has it then reads the files, the watching part is handled by the OS, so I'm not sure of the specifics. As far as I'm aware your software only writes to the modem log once per minute, so they can't clash.
I run the GUI 24/7 on my server, I also run it at work, and have never had this problem, nor am I aware of anyone else which suggests it's something specific to Korbens setup.
Edit: I've just checked the actual program and the watcher fires an event which runs the code to read the file when the modem log has been written to. See
here for more info.
So my code is triggered when the modem log is written to, it will first read the modem log, then the xlogfile, and takes mere fractions of a second to complete the reads of both files.