Is your allowable stress jumping to a much higher or much lower allowable? If so, I still believe the program may be listing a different check - going from axial stress controlling to hoop stress controlling. The limit for hoop stress is the hoop allowable while the limit for axial (bending) stress is based on total allowed axial stress at the current hoop pressure minus the axial stress due to pressure.
I have no other guesses to offer without more information about your model.
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Dave Diehl