Plants have no problems receiving and processing blue spectra light however the red part of the spectrum is quite weak. So when you switch to flowering you are telling the plants by the 12/12 light cycle that its coming to the last phase of its life and that is to flower in readiness for pollenation. Nature triggers this by the change in hours of sunlight per day being shorter, and less blue light and more red light in sunlight over the late summer early autumn.
Plants have adapted to this by using the ample amount of blue spectra and the lesser available red to grow lots of leaves, and when the photo period hits as low as 12/12 of light and darkeness they have chemically become adapted to expecting more red spectra light for food proteins and energy to grow their buds.
6500k CFL bulbs have a little red in them but not enough in the balance of things to match what your plants would expect during the flowering phase.