Mask of a Thousand Faces

Vampire X has card text +1 stealth.
Vampire Y has card text +1 bleed.

From what I can read out of the rulings, vampire X can use Mask of a Thousand Faces to take over a bleed action started by vampire Y, but vampire Y can not use Mask of a Thousand Faces to take over a bleed action started by vampire X.

Why does only one of these effects stop other minions from using Mask of a Thousand Faces, what makes them different from each other?
(I understand that stealth and bleed are different effects, but not why they're handled differently by Mask of a Thousand Faces.)
Is there a list of these "other effects" that disables the use of Mask of a Thousand Faces, or some way to tell them apart?

Rulings wrote:

The action remains the same (same level, superior or inferior, same parameters, etc.). All action modifiers remain in effect, but inherent modifiers (a minion's inherent +1 bleed or +1 bleed from a Laptop, e.g.) do not. Other effects applied to the action (e.g., Backways, Deflection) also carry over to the new (masking) vampire. [RTR 19951110] [LSJ 19971201] [RTR 20030519] [LSJ 20030520] [LSJ 20030521]

Rulings wrote:

Mask cannot be used to mask an action if the Masking vampire is not capable of taking that action, nor if any action modifiers, reactions, or other effects (including inherent stealth) have been played on this action that could not have been played/used if the Masking vampire were the acting minion. (Not counting blood that has already been spent.) [RTR 19980623] [RTR 20030519] [RTR 20041202]

Name: Mask of a Thousand Faces
Cardtype: Action Modifier
Discipline: Obfuscate
[obf] Only usable by a ready, untapped vampire other than the acting minion who is capable of performing the action. Not usable if any action modifiers or other effects have been used that could not have been used if this vampire were the acting vampire. Untap the acting minion and tap this vampire instead. The action continues with this vampire as the acting minion.
[OBF] As above, with +1 stealth.

Ankha wrote:

It's because:

• +1 stealth effect is immediatly applied when the action starts.
• +1 bleed effect is only applied when the action resolves.

So you can't Mask the action in the first case because built-in stealth effect can't be masked, but you can Mask the action in the second case because the effect hasn't been used.

But the +1 bleed effect should be announced when the action starts, just like the +1 stealth.
By the same logic, why doesn't the +1 stealth only get applied when resolving blocks? Technically, before any block attempts the +1 stealth hasn't been "used" either. Both effects (+1 stealth and +1 bleed) could be seen as incentives to block/not block, bounce/not bounce etc so I don't think the argument that one might chose not to attempt to block in the +1 stealth case really holds up.

Are all +/- bleed modifiers only applied when the action resolves?
Is this covered in the rules somewhere?

henrik wrote:

But the +1 bleed effect should be announced when the action starts, just like the +1 stealth.

Real-world logic : you believe the people to have +1 bleed, it's only once the action is masked that you discover it was not the same people. But you can't "believe" the action being more stealthy than it was..

I understand that real world analogy does not give rule explanation

@Henrik:
When you tap the vampire, they use the +1 stealth. The action immediately gains the additional stealth and not when a block attempt is made.

When you tap a vampire with +1 bleed, they don't 'use' the +1 bleed until the action resolves. It's not 'actually' +1 bleed until the action resolves (until then it attempting to bleed with +1 bleed).

Juggernaut1981 wrote:

@Henrik:
When you tap the vampire, they use the +1 stealth. The action immediately gains the additional stealth and not when a block attempt is made.

When you tap a vampire with +1 bleed, they don't 'use' the +1 bleed until the action resolves. It's not 'actually' +1 bleed until the action resolves (until then it attempting to bleed with +1 bleed).

This is a repeat of what Ankha already said.
I understand that the +1 bleed only has any real effect when the action actually resolved, but that doesn't mean that the action doesn't have a bleed amount until the resolution. There might be a ruling to say that though, but I can't find it in the rulebook, complete rules reference or old LSJ rulings. If there is anything there that I have missed I'd love a link, I'm asking because I'd like to understand how Mask of a Thousand Faces interacts with different effects in order to be able to rule on future unforseen situations. Getting illogical (to me at least) answers without any rulings behind them doesn't help much with that, neither does "real-world logic".
Sorry about that.

But either way... Just like bleed amount is, in a way, irrelevant until the resolution of an action, so is stealth irrelevant until block attempts are being made. I don't understand why +bleed would work differently than any other +whatever modifier and only get applied later during the action instead of when the card/effect is played/announced. And as stated, if the answer is as simple as "because it's different", I'd love for that difference to be implemented into the rulebook and the complete rules reference (or pointed out to me in case I've just missed it, which could happen).