She/they are trying everything they can to have one last go at reproducing/seed making, before dying. Usually stress induced, in older, over ripe flowers.
Watch for "bananas" too, they will also be produced once the flowers are as old and over ripe as these. Even if you do find "bananas" the chance of any seeds developing are almost zero, for once the flowers are as ripe as these, death is imminent. You must enjoy really heavy sleepy pot! Way too ripe for my preferences!
I usually harvest when only the last 5-10% or so of the pistils remain white as this is when THC is at its highest level. These flowers would now contain a decreased THC level and increased CBN and CBD levels, and this is what produces the heavy, sleepy effect. To each there own! Hope this helps... Organoman.