Yes its real common with clones, Im not really sure why they do that for just about everyone. But it happens a lot, I am a member of a lot of forums and Ive read many posts like this this year. A clone is already sexually mature and the shock from going from 24 hours or 18 hours to outside puts them into flower just about everytime it seems like. They will probably re-veg on you, when the one-finger leaves start growing, you know its starting to re-veg, then its up to you what to do.
1. Let it re-veg and harvest in fall.
2. Find a way to keep it in flower like putting a garbage can over it for a few hours until it gets dark everynight(try to simulate 12/12)
3. Harvest pre-mature herb.
Option 2 would be a pain in the ass if its a guerilla grow and bad for security possibly. If you got them in your backyard it would be a lot easier to do that obviously.
Im not real experienced with growing clones but maybe next year buy them in late June or early July, or leave them in the house vegging until then. I dont know, maybe someone can help you more with this, as I dont really have much experience growing with clones outdoors. I do have some experience with bigger plants from seed doing this in the spring and it sucks, re-vegging usually leaves you with stringy buds in the fall, not sure how it works with a clone but I imagine its the same.