A bidding "misunderstanding"

NORTH ª Q 8 2 K 7 4 3 10 9 5 § A K Q     SOUTH ª A 9 6 3 A Q 5 A 8 3 § 9 8 3

North 1NT 2NT* 3NT Pass South 2§ 3§* 6§

My partner (egil) and I sat impassively through this auction, and it was surprising to find that the contract went down by four tricks!!!
And this was an expert pair!!

What happened?

2NT -


• alerted by North as "no 5-card suit, no 4-card major"
• alerted by South as "no 5-card major"

  3C -

• alerted by North as "minor stayman"
• alerted by South as "further enquiry"

  3NT -

• alerted by South as "5-card clubs"
  

  hee hee.