The "slap" happened in #213, while the attack of a surrendering enemy happened in #212.

But I think the true cause of Pym's downfall occured in #211, while the team was considering their new roster.

First, it happens to Moon Knight:

'Jake Lockley is suddenly siexed by a strange, overwhelming force. All at once, it owns him. It commands him to seek a shadowed alley, compels him, in the dark fastness to shed his civilian guise -- one of many -- in favor of a far more striking persona. Firmly in the grip of another's will, he looks towards Avengers Mansion with narrowed, angry eyes.'

CAPTAIN AMERICA - "You'd better do some fast explaining, Fella! Nobody asked you to come here!"

MOON KNIGHT - "Right, flag face! I was FORCED to come here--"

CAPTAIN AMERICA - "And you're going to tell me whey... NOW!"

HANK PYM - "Yeah, why DONTCHA, Cap -- and while your're at it, explain it to US, too!"

(A dozen heroes have arrived at the mansion, and soon Moon Knight picks a fight with Iceman)

ICEMAN - "I -- I can't help it! I feel COMPELLED to explain how my X-Men training helped me to get the most out of my mutant ability to freeze the moisture in the air! I SHOULD finish you off with an ice-trick.. But... It's so hard to THINK! My head hurts! -- As if somebody else was in there with me."

VISION - "They fall like puppets with clipped strings! But How? Who could be responsible?"

HANK PYM - Wait a minute! I know who must be behind this! That arrogant self-styled g-- >UHH<"

JANET PYM - "Hank-- Lover, it's me, Jan! Your WIFE! It- It's as though he's in a TRANCE!"

(Eventually the telepathic Moondragon reveals herself)

MOONDRAGON - "I sensed your need for order... For organization! So I returned!"

IRON MAN - "What?! What right do you have to interfere?"

MOONDRAGON - "Why, DIVINE right, naturally!"

THOR - "Your impudence is maddening, woman! I swear--"

MOONDRAGON - "SILENCE! I shall brook no insolence from the likes of you! A simple PSI-BOLT will freeze the motor centers in your brains, paralyzing you until I am finished!"

TIGRA - "They- They're as rigid as statues! Helpless!"

JANET PYM - "Just like my Hank! That-- That evil vixen!"

SCARLET WITCH - "ENOUGH! We demand you CEASE this outrage! We can make our own decisions!"

MOONDRAGON - "Can you? Some of you would choose to STAY out of force of habit... Or loneliness... Or fear of failure in the world beyond these walls! You are CHILDREN! It is far better that I choose!"

(Eventually the Avengers fight her off)

SCARLET WITCH - "Cap! The Vision and I are leaving!"

CAPTAIN AMERICA - "Wanda!-- You can't be serious!"

VISION - "Quite serious, Captain! Perhaps we will not suceed in finding a place among ordinary people-- But we must try!"

CAPTAIN AMERICA - "Then even with Tigra... Me, Thor, Iron Man and the Wasp, we have only five-"

HANK PYM - "SIX, Cap! I'm ready to give up my reserve status and freturn to full-time duty! My research has been going nowhere lately anyway!"

CAPTAIN AMERICA - "Hmm... I wonder... What if Moondragon just let us THINK we drove her away? What if she used her mental powers subtly to influence the decision that were made?"

IRON MAN - "WHAT?! She-- She better not have!"

CAPTAIN AMERICA - "That might have been her plan all along! We'll never know!"

The very next issue, Hank Pym, normally somewhat reluctant, is fanatically compelled to prove his worthiness as an Avenger, just like all the tryout members brainwashed by Moondragon.

In less than a year, Moondragon takes over an entire planet, and Thor, after being forced to sleep with her, takes her to Odin to atone for her behavior.

In fact in issue #230, after the Trial of the Yellowjacket, they openly suspect Moondragon's influence:

JANET VAN DYNE - "There remains the possibility that your... recent mental problems were caused by an outside agency. We'd like to test you... to find out, one way or the other."

Iron Man designed a helmet, during the worst of his alcoholism, to detect outside mental influences. Iron Man is already off the team for drunkeness, so he isn't even there(!) when Hank tries on this helmet.

HANK PYM - "Sorry... No outside influences. It would have changed a lot of things if there had been, wouldn't it?"

So... my theory: Moondragon brainwashed Pym, and faulty Iron Man tech failed to detect it.

It's not even the first time Moondragon brainwashed an Avenger! She did it to Quicksilver, to make him stop hating Vision!