Exactly!! You nailed it! After testing with that in mind, it proves to be as you say...
Since I have been dealing with tuplets in my latest reports, take a look at this :
https://www.dropbox.com/sh/h0o73cimz...bZFbBiZta?dl=0
After moving the bracket from the low voice tuplet, the first note of the high voice is messed. Broadly speaking, tuplet brackets handling seems to be visually confusing most of the times. Whenever you move them above or below, the brackets themselves remain between the notes. I hope there can be a cleaner way at some point...