Yes, using shadow strike on the sides instead of the back seems to work.
The thing with spinning strike is that it starts the animation but doesnt quite finish it, I'm sure if you lack the force to use it or the target is not low enough on hitpoints you never even start the animation. It doesnt happen too often though.
Honestly, I wasnt really expecting the vanish type spell to work properly from the start anyway. Resilience doesnt even remove certain debuffs, like that bomb with timer on it that bounty hunters use ( I guess it's not removable). Force cloak might also suffer from that issue where abilities just wont go off, which seems to be fairly common.
Having complete immunity to damage in vanish wouldnt be good, I agree with that. I wouldn't see certain amount of creativity allowed with how the abilities can be used as a bad thing. It's actually what I was expecting from this class. I realize you meant it as in abusing slightly broken mechanics which is a bit different thing.
How vanish works in wow currently seems ok, stealth doesnt break from damage for 3 seconds after using it but you're not immune to damage. Still need to clos dots for a clean vanish but it gives a lot more room to work with. Different game but anyway.