Hi,
Yes, it is a known issue, affecting some installations. It will be fixed within the next bugfix update.
To manually fix it for now, you can follow these steps:
1. Make sure to have a back-up of everything before editing the files.
2. Open up the wp-content\plugins\ajax-search-pro\includes\classes\filters\class-asp-searchoverride.php file via FTP
3. Replace it’s contents with this.
4. Save the file.