LST Harmful?

Just wondering if anyone else has experienced broken branches from low stress training?
I had one of my plants snap a branch that was tied down. When I bend and tie I use soft plant ties and never once have I even came close to breaking any branches. It was just really weird.
I came in to check on them and one of.my branches was mysteriously snapped and barely attached to the plant! I had to cut it off and was still able to get a viable clone from it so it wasnt a total loss.
Just really strange, ive never seen one do that before. I wonder if the strength of the plant was so great that while trying to reach back to the light, it broke.

Thoughts?

Can you take a picture of the plant? In their younger stages need to be careful, they will get stronger. But really to help pictures and more of a background of how you are growing can help. Are you using a fan as well (Sorry again, know nothing of your set up).

Aurora Indica
med: ffof soil
lights: 600w mh 20/4
Temps 72-74 deg F
rh: 40-50%
Plants are about 6 weeks old, from seed

Notice that ive main lined them. Just did the final topping yesterday for 8 colas per plant.They look good and except for "tripod" have responded well to training. I havent bent them anymore, stems are too thick now..waiting for new stems to get a little longer before I attempt to shape them anymore. Dont think I really need to, being indicas, theyre not gonna get much taller in veg. Im kind of gun shy about it now.

I've snapped a branch off before, so in that sense it's harmful haha

I got this girl to do a split by accident, she's doing great though

Just seems odd that a plant would pull a branch so strongly toward the light that it would actually injure itself. I couldnt believe it.

This happened to me last year. I watered them in the morning then went out arround noon and LST them (after watering they become much easyer to bend) but it was a really hot day and when i went to check them that afternoon i noticed 1 branch broke just hanging there.
The soil was pretty dry compared to when i LST it.

Only thing i can think of was the moister escaped to quickly and snapped. I propped it up and used electrical tape and a splint and by a the next week it was healed and standing on its own.

Strange but wunderful plants