[Plugin: W3 Total Cache] Access forbidden and file permission errors

When I turn page cache on, it generates html and gzip files, however the permissions on these files are sometimes incorrectly set.

Most often, permissions are set to 644, which works well. Sometimes, however, both html and gzip files get permission 640, which prevents non-registered users to read and access those files, and users of the blog just get the 403 Access Forbidden error.

Any suggestions?