Yosemite bug
Theres definitely a bug in Yosemite and Millumin 1.51 where the transform/mask/warp box disappears.
Restarting Millumin fixes it. I've attached a screen shot of the bug, then straight after restarting.
Comments
I don't think it's a bug : you're on the last frame of your composition, so your media probably ended on the previous frame.
Best. Philippe
PS : please report bug on contact@millumin.com as it's easier to manage for us