Issue when moving notes on Drums from Midi File

Hello, I am experiencing a weird behavior that seems to be related to voice assignment / midi import.
1/ Open a drum set midi file
2/ Select all, copy, and paste in a flow on a drum set staff
it works great but when I move the notes around in write mode, this happens:
before moving.png
after moving one step down.png
I only experience this behavior for triplets and tuplets. Could this be a bug from the midi import?
I don’t even understand this notation, is there a way to fix this?
Any leads would be greatly appreciated!

There is one thing that strikes me in your first picture : the 3 of the triplets are not selected. This means “trouble”…

thanks Marc, you’re right that’s usually a source for problems
but in this case, even if I select the triplets, there is is still a weird thing happening

it seems like the bug is not coming from the midi import but from a copy/paste of tuplets from a non-percussion staff to a percussion staff