Unability to select individual sounds within non-GM soundfonts

Hi there,
I usually use an organ sound bank under MS3.6.2 "Orgue de salon.sf2", which can be found here: http://sonimusicae.free.fr/orguedesalon-en.html
This sound bank has intrinsically many elementary organ stops, for example "Bourdon+Flute4".
I imported the entire sound bank under MS4. Musescore detects it without any problem in the choice of instruments in the Mixer, but unfortunately I no longer have the possibility of choosing one of the many individual organ sets offered in this sound bank.
It's a shame, I see this as a regression MS4 vs MS3.6.
Have any of you seen this issue before?
Will this be fixed in a future MS4 update?
Thanks a lot for your help.
Rémy
(from France)