The white wing-like piece continues to pop off when placed. Has anyone figured out a fix for this or am I doing something wrong 

**** http://imgur.com/ZzKrBse,FjqA6IE#0**** Subset 3-4 


<img src="http://lego.brickinstructions.com/10000/10234/163.jpg" width="500" height="636">

Thanks for the reply how you can figure it out im stumped