Notation of "voices": 1.voices that share a note; 2.voices that change staff

Hi
I've been trying to notate correctly (for piano) a phrase very similar to bar 35 of Bach Prelude no. 2 in Book 1 of the 48 Preludes and Fugues / Well Tempered Clavier where the left hand bottom C is shared by two voices and is notated by the bottom C having both an "up" and a "down" note stem (see attached Bitmap image).

I couldn't find how to do this in the manual but I found the following method:
1/ Enter notes for the correct values (they don't need to be the correct notes) for all bass clef voices so that they show across the measure as separate voices
2/ Select one of the voice notes that needs to be "shared" then "merge" it with the other voice using the Up/Down keys
3/ Clicking on the "shared" notehead will NOT then show the voice colour - the notehead will remain black - but by using the Up/Down keys the voices can be separated again to show the colours if needed for subsequent editing.

Perhaps this could be added to the manual for other users?

However, there is a problem with the cross staff beaming. If you compare the Bitmap image from the published Bach score with the attached Musescore extract you will see that the stem of the first note (the B natural in the right hand) is down instead of up, and pressing "x" to flip it does not work. I know this is "only" a visual thing but for musicians the "look" of a score is important to make sense of it. Is there a way of getting the note stems in cross staff beaming to display correctly?

Thanks.