I wonder if this is actually being caused by Task scheduler, especially looking at Darrens isrunning time stamps. There is a known bug with task scheduler, basically task scheduler creates a list of scheduled tasks each hour, so it's possible for a task to be at the end of that list, and be scheduled incorrectly at the start of the next list, hence Darren's isrunning files being every hour, at least that's my thinking.
This has been mentioned before, but as there was only one isrunning I'd sort of dismissed it, but the first logging task will run OK, but if another logging task fires whilst it's running that will see the other one running and leave an isrunning file.
See here for an MS Hotfix - usual caveat - users try at their own risk.
I am also one of the users that had recently had problems, I had 18,000 isrunning files on my server, the problem occurred several weeks ago and I simply hadn't noticed my logging had stopped until Saturday
The fix BE has just rolled out should remedy the problem I had. It also seems my scheduled task was also running at the lower priority, using the higher priority task I've had no isrunning files in the last 24 hours.