It was a regression introduced in bash-4.4 that was fixed by http://git.savannah.gnu.org/cgit/bash.git/diff/parse.y?h=devel&id=5bf9b550c0adec566a39b7c5ccad6c8270e7d001
https://src.fedoraproject.org/rpms/bash/pull-request/5
bash-4.4.19-2.fc28 has been submitted as an update to Fedora 28. https://bodhi.fedoraproject.org/updates/FEDORA-2018-19927d07f2
bash-4.4.19-2.fc28 has been pushed to the Fedora 28 testing repository. If problems still persist, please make note of it in this bug report. See https://fedoraproject.org/wiki/QA:Updates_Testing for instructions on how to install test updates. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2018-19927d07f2
bash-4.4.19-2.fc28 has been pushed to the Fedora 28 stable repository. If problems still persist, please make note of it in this bug report.