Actually, when using bleach to oxidise the KI into I2, chlorine gas gets formed insitu no matter what (I beleive). SWIM always smells a little when he adds bleach to precipitate the I2. If the amounts of ingredients you added is in decent ratio to one another (as in closest to the required stoichiometric amounts) then the Cl2 gas is never really noticed. Sometimes if things get a little wack and you overdo it on the chlorine you'll smell it more. That is because SWIM beleives the mechanism of the bleach/HCl/KI rxn something like this:
1 NaOCl + 2 HCl----> 1 NaCl + 1 H2O + 1 Cl2
1 Cl2 + 2 KI---->2KCl + 1 I2
So you can see when using bleach chlorine is formed insitu, and is what actually oxidises the I- ions from the KI.
It seems to survive when in solution with Cl ions all over, as is the case if it's in solution with HCl
Those are ions though. Basically reduced (as in addition of electrons) chlorine is Cl- ions. Chlorine is a very strong oxidant (all halogens are oxidative, some like chlorine are way more so than others, like I2, gaseous chlorine is oxidative enough to support combustion without the presence of oxygen). This means that elemental chlorine or Cl2 will oxidise things, becoming reduced itself. This action will can cause areas of organic molecules to become oxidised, in turn making then positively charged. Since the chlorine was reduced, it becomes negatively charged, so the chlorine attatches itself to the positively charged area of the organic molecule. As far as pseudo or meth goes, one of the places most succeptible to this is the benzene ring. Exposure to halogens will cause ring halogenation. Now some halogens aren't strong enough to do anything at all without some sort of catalyst, some will only react a little without catalyst, some don't need a catalyst at all.
Ions are already reduced, so a solution containing meth or pseudo that also has a plethora of Cl- ions will probably remain unaffected.
