Is Rails Logger truly not Thread Safe? http://log.kares.org/2011/04/railslogger-is-not-threadsafe.html
This seems like an issue that should have been picked up quite a long time ago. I just set config.threadsafe! in my config/application.rb and my log output from rails server has completely disappeared.
It looks like someone tried to fix that around a year ago - Fix threading issues with BufferedLogger. · rails/rails@d565fda · GitHub
What version of rails are you using ?
Fred