Changing soundfonts doesn't seem to change instruments

Following the documentation, I changed the soundfont from the default (TimGM6mb.sf2) to another one (FluidR3_GM.sf2). I changed it using the synthesizer window, closed MuseScore, then re-opened it. The synthesizer window showed the path to the new soundfont.

When I tried to use the instruments, I got the same ones as in the default. When I went to Staff Properties, Create Instruments, or Change Instrument, the default instruments appeared. Only when I opened the mixer window did I see the instruments in the new soundfont. I find this behavior puzzling.

Is there some reason why this happens? Is it a misfeature? I would appreciate any information that might clarify this for me.

Thanks.

-Baruch