I have actually had several friends ask me how it works, meaning does it add charges
In other card games for example Magic the gathering card who take control of cards and make them be able to attack right away will say that it gives them haste. Usually it says untap(so it can attack/block) and give it haste.
And yes yes, Hearthstone is not magic. But Priest do have 2 more take control over cards. Cabal Shadow Priest and Mind Control
So when a player take controls with Cabal Shadow Priest can they attack with the minion right away? Yes if its a Bluegill Warrior as it has Charge. Otherwise no, same with Mind Control
Here for example a Priest toke control of my King Krush and attack with it right away as it has Charge otherwise he could not have done that. (He also managed to kill himself doing it ;)
So Cabal nor Min Control has that they add charge.
However, Shadow Madness does add charge to the minion the player takes control of.
Its not cut clean that it has to do that, sure it would be a pretty shitty card otherwise but given priest has a lot of bad cards would anyone be surprised? It woulds still has some use for e.g removing a taunt to win the game etc.
But yeah I am not debating that Shadow Madness works like it should but the text is incorrect.
And like I said in the start, really a lot of people has asked me how it works as most of them come from a magic the gathering background and then they would not expect it to give charge on the same time they are intelligent enough to assume that a 4 mana temporary control with no charge seems of.
Lastly
The card text is pretty long on Shadow Madness so one might argue and say how can they fit this added text. Well I compared my change to the card text on Void Terror card, will still have 5 more characters in its text even after my suggested change to Shadow Madness. As one can see on Void Terror they can just use smaller font.
Change from:
"Gain Control of an enemy minion with 3 or less Attack until end of turn"
to
Gain Control of an enemy minion with 3 or less Attack, it gains Charge until end of turn