Relevant issue on RawTherapee BTS: https://github.com/Beep6581/RawTherapee/issues/3154#issuecomment-215243911
Seems like this bug happens with latest Fuji's firmwares but everything's fine with the latest version. Not relevant but worth considering for next deb packages: it seems like RT is switching to gtk3 as a default. Thanks! -- Leonardo Canducci