ibus-gtk[2|3] have depended ibus not to break the API compatibility between ibus and ibus-libs since some applications could require ibus-libs only without ibus. Actually ibus-libs does not require ibus but needs to keep the same version between ibus and ibus-libs. Now I think 'Conflicts:' tag is the right usage for the purpose and will delete 'Requires: ibus' in ibus-gtk* and use 'Conflicts: ibus < version' in ibus-libs.
ibus-1.5.19-6.fc29 has been submitted as an update to Fedora 29. https://bodhi.fedoraproject.org/updates/FEDORA-2018-5f24d1ee9d
ibus-1.5.19-6.fc28 has been submitted as an update to Fedora 28. https://bodhi.fedoraproject.org/updates/FEDORA-2018-998a7b6fc3
ibus-1.5.19-7.fc29 has been submitted as an update to Fedora 29. https://bodhi.fedoraproject.org/updates/FEDORA-2018-5f24d1ee9d
ibus-1.5.19-7.fc28 has been submitted as an update to Fedora 28. https://bodhi.fedoraproject.org/updates/FEDORA-2018-998a7b6fc3
ibus-1.5.19-7.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-2018-998a7b6fc3
ibus-1.5.19-7.fc29 has been pushed to the Fedora 29 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-2018-5f24d1ee9d
ibus-1.5.19-7.fc29 has been pushed to the Fedora 29 stable repository. If problems still persist, please make note of it in this bug report.
ibus-1.5.19-8.fc28 has been submitted as an update to Fedora 28. https://bodhi.fedoraproject.org/updates/FEDORA-2018-998a7b6fc3
ibus-1.5.19-8.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-2018-998a7b6fc3
ibus-1.5.19-8.fc28 has been pushed to the Fedora 28 stable repository. If problems still persist, please make note of it in this bug report.