Trouble with duplets & voices?

I'm working with 9/8 time, & I wanna have a bar with two voices, where only one voice has a sextuplet across the entire bar.
I've tried two ways: (1) make a sextuplet first, then add a second voice; (2) deal with the first voice, then add a sextuplet in the second voice.
(1) doesn't work: nothing happens when I try to add voices to the tuplet.
(2) doesn't work: since it's 9/8 time, there's no single rest notation that counts the entire bar, so I can't add a sextuplet that occupies the whole bar.

Right now I'm using 3 duplets to substitute the sextuplet, but I'd like to know if it's a bug, or there's a workaround for this. Thanks!