Sometimes a trap will catch an insect that is too big for it to digest before bacterial decay of the insect begains to take place.
When this happens the infection spreads to the lobes, and will eventually kill the trap.
However it would appear that the portion of the trap as yet unaffected by the mould continues to secrete enzymes and digests what it can of the insect before it succumbs to the infection. The spine of the trap and the stalk are always the last sections to be affected, that would indicate the plant has evolved to extract as much nutrient as possible from every successful trap.
Even though decay has taken place, the trap remains sealed, this allows the unaffected portion of the trap to function as normal.