Magnolia bush leaning after rainfall

Hello,
I'm new to this forum. I live in the Fraser Valley (suburbs of Vancouver, BC).
I have a magnolia bush in my garden that is about 10-12' tall. I planted it as a baby in April 2013, when it was just a little bit taller than knee height.
It's a bush rather than a tree, it has four separate trunks that are around 2-3" thick, rather than a single tree trunk. On Friday evening, July 6, we had a heavy rainfall with wind, and when I woke up Saturday morning, the entire bush was leaning over toward the patio. I tried to shake some of the rain out of the leaves, thinking that maybe it had been overwhelmed by the amount of rainfall. It persisted in leaning, and only stood up again fully after it dried out and I trimmed off some of the very heavy branches.
Is this normal for magnolia bushes? Should I be staking it?
Any help would be greatly appreciated.

 

Just wanted to bump my question. Has anyone experienced drooping/leaning of a magnolia bush after rain, where it didn't seem to want to stand up by itself again without help?

 

Probably root-bound due to careless container culture at a production facility - look at the bottom of it to see signs of it having pivoted over on a wad of circling main roots. If this scenario appears to be in effect then you will have to install a post to which the tree can be secured, in order to get it to remain upright.

Or maybe try pushing an adequately large rock up against it. In either case you will be likely to need help with getting and keeping an 11 ft. top in place during the operation.