Cast Bloodletting on Madora and if she fails the saving throw against Bleed, it will do a significant amount of healing. I think that, at least, is not working as intended.
Since the healing amount is independent of the volume of blood, if a leech runs after a moving character that is bleeding, they will heal much more than letting the character bleed and then run over the blood surface.
Unfortunately, this doesn't really answer the question. I think the question is, should regular physical attacks cause Leech to proc?
It is working as intended. Leech basically uses any blood source to heal you. The only thing may/may not be intended is the way bleed works.
When your toon bleeds, she is soaked in blood. Bleed only procs one per turn AND if your toon is soaked in blood. Leech removes the blood and as a result, bleed keeps proc'ing until she is healed to full and is soaked in blood again.
And this is exactly how poison and burning work. The damage is incurred in all three cases when your toon's body is soaked with blood, poison or doused in flame. That is why when you set a poisoned npc/pc on fire, the poison is consumed to make explosion and poison damage keeps proc'ing.
Unintended consequences maybe but the mechanics is exactly how it should be.
Hold on now...
First, the semantical argument here (that I won't dive too far into) is that standing in blood in D:OS does not necessarily mean soaked in blood, since in D:OS standing in environmental effects is a big deal and an important mechanic. There is room for ambiguity, and based on the description of the Talent, one could argue that if you're not actually standing in visible blood on the ground, then Leech shouldn't proc.
Basic physical attacks (melee and ranged) proc Leech without any environmental effects (ie pools of blood) being produced, and that seems weird (even if, in real life, when you get hit by a sword you're probably going to bleed; real life is mostly irrelevant here).
Second, in the latter part of your post you seem to be defending the mechanic according to the status effects Bleeding, Poisoned, and Burning. But this just further illustrates the question/problem at hand: regular, non-skill physical attacks do not apply the Bleeding status (otherwise there would be very little point to Bloodletting and Draw Blood inflicting that status themselves), and yet basic physical attacks are proc'ing Leech. And they're proc'ing it with each and every attack, not just once per turn as it would be with Bleeding.
Also, Poisoned and Burning work very differently than Bleeding. You can walk in poison and fire and pick up their respective status effects. When you walk in blood, you don't pick up the status effect Bleeding... so they're really not the best defense of Bleeding/Leech.
What are the ways in which Leech >could< proc?
1. Walking through an environmental puddle of blood. This basically makes since with the mechanics of environmental effects and the talent description.
2. While under the effect of Bleeding. This makes sense because if you have this status effect you are probably soaked in blood (and it would work like you described, haxing).
3. After being hit by a regular physical attack that generates a blood pool underneath you. This makes sense according to #1. (Granted, I think that such pools of blood should be limited to critical hits)
4. After being hit by a regular physical attack that DOES NOT generate a blood pool.
#4 is what the OP is questioning (I think, and if he isn't, then I am): is this intended?
It seems to me Bleeding is a status effect that operates in different and confusing ways in comparison to the others. So why not bring it in line with the others? Like you would with the other status effects, when you walk through a puddle of blood you potentially pick up the "Blooded" status effect (ie, being covered in blood). Bleeding inflicting skills, instead of causing Bleeding (which, let's be honest, doesn't really seem to have a tactical use and is rather weak) causes a target to be Blooded... which could then lead to detrimental effects from other spells or the environment. I don't know, maybe being Diseased becomes easier or something.