Hi!
The only option that should affect this is the search override. Make sure to enable that, and use the GET method.
If that does not work, then check if you have any other search plugins active that may affect the results page in any way. If not, then it is very likely that the results page uses some sort of a custom query, that completely overrides the passed results. In that case, you can add temporary FTP details, and I can check on the affected theme code section, but there is no guarantee I can fix that. Worth a try though.