Have done some testing within KTD to make sure it is an upstream bug. Essentially if you are searching for a particular author, say for example Dennis O'Driscoll and you also have items from another author by the name of Dennis O'Malley If you search for O'Driscoll and use the "Refine your search" feature to select titles only by author Dennis O'Driscoll, you'll be given results by both Dennis O'Driscoll and Dennis O'Malley. After further testing I have narrowed it down to the apostrophe being the reason for this, I haven't figured out why just yet but it's a start. I have tried this on both 24.05 and 23.11 and the behavior is consistent.
To add to the versions I have seen this bug present on, I tried it out on a 23.05 instance just in case it may have been related to https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=27153 but the behavior still remains