Kindred's on-hit deals a minimum damage of 8 damage per stack, and other missing tooltips
Tested this in across several games, seems quite consistent. Its ~ 8.25 damage minimum per stack with my masteries, and I believe exactly 8 without them. This means that if your target has less than 640 hp, it deals damage as if they had 640 hp.
This is missing from the tooltip, as is the fact that you need to wait about 10 seconds after you mark someone before you can collect your stack.
The damage is also uncapped vs monsters, with all the cheese that entails.