forked from: swf.hu: 3D forgatás közben startDrag - the solution

http://www.swf.hu/forum/topic/3d-forgatas-kozben-startdrag

http://kb2.adobe.com/cps/901/cpsid_90194.html :
"...
Known issues: ... 
- startDrag and stopDrag do not work when the target is a 2D child of a 3D parent. (2200972)
..."

the solution:
childObject.z = childObject.z;
or (if you don't prefer "meaningless" code at first sight):
childObject.z = 0;