It could be a number of things which are keeping the file open, e.g.

* Windows indexing the volume for search
* Child process keeping files open (e.g. while copying log files - I can't tell what you're actually copying)

You may need to use a tool like FileMon or PSMon to see what's happening, but I don't see any evidence that it's a logging bug.

Is there a specific logging statement which is being called which leads to the error? There are several in your snippet.