Bougainvillea leaf drop question.

[Ironbeaver]

My bougies are doing something I haven't seen yet. They (all rooted cuttings + the mother plant) are dropping lots of leaves all of a sudden. Now, they seem to be throwing new growth from the locations of the drops but I'm just trying to figure out what is going on.
Things that have changed:

1. Weather is getting colder, cold air is coming into the solarium (temps stay between 22C(68F) and 25C(77F)) the colder air is a bit of a "draft"
2. Started using "new" fertilizer, used up the 5 year old stuff I had before
3. Forced air heating has come on, air may be drier (waiting on delivery of a hygrometer)

I haven't been doing much to them, just growing them on, although I did snap on cutting while testing flexibility.

Any ideas?

 

[CWTurner]

My bouganvilla did the same thing this fall when I brought it indoors for the winter. I assume this is typical, like with ficus, when their exposure is changed.
CW