Error expressing Jack symmetric functions in terms of power sums

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I'd like to express Jack symmetric functions in the J basis in terms of power sum symmetric functions. Here is an example of how I've been doing this.

F = FunctionField(QQ,"t")
Sym = SymmetricFunctions(F)
p = Sym.p()
JJ = Sym.jack().J()

p(JJ[3,3,1])

This example ^ works just fine. My issue is that once the partitions get to be a certain size (namely, 9), I get a key error.

F = FunctionField(QQ,"t")
Sym = SymmetricFunctions(F)
p = Sym.p()
JJ = Sym.jack().J()

for n in range(2,11):
     for llambda in Partitions(n):
          try: 
               p(JJ(llambda))
          except KeyError:
               print(llambda)

What exactly is going on here? Why can't [9,1], for example, be expressed in terms of power sum symmetric functions?