OWSTimer holding usage files in memory; unable to delete through timer job

I have a couple of farms (#1 = 2010 Enterprise, SP1 w/ June 2012 CU; #2 = 2010 Enterprise, SP1 w/ Dec 2012 CU) and I'm having the same issue in each.

The timer job to import usage files (job-usage-log-file-import) is constantly receiving error messages regarding a failure to delete older usage files (Failed to delete usage log file 'D:\Logs\Usage\SPDEVWEB-20130910-0726.usage' after data import. Exception: System.IO.IOException: The process cannot access the file because it is being used by another process.).

If I try to delete these manually, I receive an error of "The action can't be completed because the file is open in SharePoint 2010 Timer".

When I look at OWSTimer.exe process in Process Explorer, I can see that each log file that hasn't been delete is still being held in memory.  The only way to clear these files is to restart the OWSTimer service on each server, which doesn't seem to be the correct solution to this issue.

In the larger farm (#1), the OWSTimer services has consumed a large number of private bytes by holding these logs in memory and over time the usage logs are filling up the disk drive as they are not being properly cleared.  It took less than 1 month in farm #1 to consume 87 GB of space just for usage files.

Has anyone else experienced a similar issue or can provide a resolution?  Any help is appreciated! :)