It looks this has already been fixed: https://bugs.launchpad.net/openlp/+bug/969282
It will be in version 1.9.10 which should be released at the end of next month. If you dont want to wait until then, you can download the nightly build from the download page under the heading "Developer Downloads". Take note of the warnings if you decide to take the second course of action.
Once you have upgraded, you will need to reindex your songs. Do this by from the tools menu by clicking re-index songs.