Previous implementation can be considered as "someone randomly decided it to be" too, because it wasn't made intentionally and without any proofs from retail.
The purpose of the glyph is that if you accidentally used death grip on immuned target, it won't be wasted. It shouldn't give you more usage of death grip than usual.
Not sure about that one. It's kinda wrong too, because it would be possible to grip someone 3 times in a row.