From https://jira.codehaus.org/browse/JRUBY-6688 and further to http://markmail.org/search/?q=list%3Aorg.codehaus.jruby.user#query:list%3Aorg.codehaus.jruby.user+page:1+mid:l5s47zvynzk7ki3a+state:results jruby unlike mri emits a warning when unlinking an open temp file.

Per http://www.ruby-doc.org/stdlib-1.9.3/libdoc/tempfile/rdoc/Tempfile.html this should be acceptable behaviour.