This can happen to sativas when the primary branches (tops) that were once getting the most light, start getting less than secondary branches. When this happens the plant recognizes the change in photsythesis and promotes the new tops getting more light to the primary seeds in hope of producing more offspring.
This change requires hormones and quite a bit of energy if the change is excessive enough.
I would guess you let the tops stay out of the light long enough for the plant to make the switch, but before it had, the plant made a last ditch effort to find its light source for its tops (initiating that crazy foxtail stretch).
Then, you switched your lighting before the new primary tops had established dominance, thus your already stressed, stretched, and hirmone frenzied top got a new burst of energy to fund its abomination.
Lol, im high but hope that made sense. I have had tje same thing hapoen with my supper silver. It grows like a willow and if you done support the tops, they weep down while suckers take off that look like mini versions of your bud, without the hormone dose though