really persistent file lock

I've got a problem where connections with certain file locks do not seem to close for more then a day even on reboot / shutdown of the client.
We have a .net/C# based document processor that runs on every user session that requires it that manages to put some weird file lock on its log files that are located on users home directory's (unable to change that).
For some reason our OES11 server every now and then does not close the connection holding the log file open and users can not start the processor in the morning because it can not access its own log file.
This -occasionally- happens with normal workstations running XP but more frequently on Win2k8r2 with Xenapp although all our Xenapp servers get rebooted daily.

I would expect the OES server closing the connections upon reboot of the Xenapp servers or when the workstation is turned off for 10+ hours. It would appear it takes somewhere over 24 hours for the connection / lock to clear but I have nothing to back this up.

Can anybody explain this behaviour and/or come up with possible workarounds, I always assumed connections were actively checked to see if they were alive.

I also need to have a talk with the people where this amazing piece of .NET software came from about the way they lock files.

Thanks