Couple DB + crit ring mechanics questions

I noticed 2 strange things with the crit ring and my DB

1. Using fatal blow with a crit ring makes the 1st and 5th hit do the same damage, without the ring they are not. Any idea why this is ?
2. When I'm using mirror image, sometimes the auto kill is triggered, but the monster doesn't die. I assume it's because it triggered on a mirror image hit and so it only does a lower % of the total hp on the monster?

not having anything to do with crit ring, but is triple stab mirror image supposed to hit 2 blade and 1 dagger attack?

Most likely they coded all Mirror Image hits like doing 100% base damage, and then multiply the final damage by 0.6...

This would cause a 100% monster HP kill to trigger 60% monster HP hit... still bugged, but that would explain this...