Weird Twilight Grasp Bug

[Rudra]

I'm doing the 2nd mission in the Crossfire arc from Arbiter Leery. One of my ninjas needed to be healed, so I triggered Twilight Grasp on the +1 Crab Spider Slicer I already had targeted. This is where it gets weird. I had already shot the Crab Spider Slicer with a bow attack and the Crab Spider Slicer still had more than half his health left. Yet when I triggered Twilight Grasp, I lost my target and no heal happened. I re-clicked the Crab Spider Slicer making him my target again, saw he still had more than half health left, and tried Twilight Grasp again. This time it worked.