Half my clones flowering in veg cycle 18hrs on 6 off ???? Indoor

I have 2 different strains, a blueberry kush, and a chemdog, both bought as clones both put under T5s, 18hrs on and 6 hrs off,and even the 6 hrs off were not in complete darkness,the room had some windows and they were getting some light from that as well. They are three weeks old in plastic cups in soil,just being fed water. I was just about to transplant them and I noticed that about half of them are flowering!!! And not all one strain a mix of both strains! I asked everyone I know and nobody seems to know why. Any ideas?
and should I bother trying to revert them to veg, or should I just flower them?
please help

My guess is they are presenting preflowers. Not actually flowering. Clones are taken from sexually mature plants in most cases, hence the preflowers(showing they are sexually mature)not flowering.

Hey Supertramp thanks for the info, I took some pics for you se what you think