See the issue at upstream github: https://github.com/defunkt/mustache/pull/116 replacing each_document with load_stream in the mustache script seems to work here.
rubygem-mustache-0.99.4-6.fc18 has been submitted as an update for Fedora 18. https://admin.fedoraproject.org/updates/rubygem-mustache-0.99.4-6.fc18
rubygem-mustache-0.99.4-5.fc17 has been submitted as an update for Fedora 17. https://admin.fedoraproject.org/updates/rubygem-mustache-0.99.4-5.fc17
Package rubygem-mustache-0.99.4-5.fc17: * should fix your issue, * was pushed to the Fedora 17 testing repository, * should be available at your local mirror within two days. Update it with: # su -c 'yum update --enablerepo=updates-testing rubygem-mustache-0.99.4-5.fc17' as soon as you are able to. Please go to the following url: https://admin.fedoraproject.org/updates/FEDORA-2012-14491/rubygem-mustache-0.99.4-5.fc17 then log in and leave karma (feedback).
rubygem-mustache-0.99.4-6.fc18 has been pushed to the Fedora 18 stable repository. If problems still persist, please make note of it in this bug report.