Erronous analysis in Bridge Play Made Easy - Reese and Jourdain?

The recent discussion on squeeze books made me reopen that particular book due to the kudos for it on the thread.  Chatper 3, third hand, "Isolating a menace by ducking" offers this hand:

West
Q93
QJ108743
6
95
North
AK74
52
K753
KJ6
East
J1062
6
J1098
10842
South
85
AK9
AQ42
AQ73
D

South is declaring 6NT after West opened 3.  West leads the Q.  The authors go on to explain that you must duck a trick to rectify the timing, but can't duck the opening lead or a diamond, since that would destroy your threat in that suit.  Therefore you win the first trick an duck a .  That rectifies the count and makes only opponent able to guards the .  Upon a or a return, you test the diamonds, and you either have a simple squeeze against West if he has 4 else you have a double squeeze with the 3rd spade in dummy winning the last trick (West hold the master , East the master , hence the is a winner).

The situation gets trickier if upon winning the spade, the opponents return a spade, voiding declarer of spades.  They write:"At this point it would be incorrect to test the diamonds by playing off two rounds.  Best is to lead a third spade and two rounds of clubs.  You learn then that there is no room in the West hand for four diamonds, so you plan a spade-diamond squeeze against East.  You run the four clubs and the A, the cross to the K, and by this time East will be under the hammer."

My problem is what to pitch on the third spade.  The recommended line of play doesn't specify what to pitch.  However, you must keep the , so you must pitch a .  But if you do so, the squeeze will not operate about East any more.  What am I msising?