PHP warning in ProxyFactory when renaming proxy file

Getting a PHP Warning:

rename(**/models/Proxies_CGAF_Model_Component_Group.php.50d2dd2c079bb9.35271255,**/models/Proxies__CG_AF_Model_Component_Group.php):

in ProxyFactory line 194.

I haven't more information in the warning.

This is the moment when the ProxyFactory writes the proxy to a temporary file and then tries to rename the temp file to the correct file.

This warning appears randomly, but mostly on pages with lots of concurrent AJAX requests. I guess this happens because several requests try to write the proxy file at the same time. I get this warning but the app works fine.

This happens in dev environment, on a Windows machine.

I don't know why rename generates a warning, it should just return false... The doc doesn't say anything about warnings (except for long file names, but I checked even with the full path this is around 135 characters, not 255).