How to integrate 2 libraries?

I have in my project sometimes need of integrating 2 flas.

I organized my symbols in folders… But when I drag one folder from one fla to another… all the bitmaps in that folder jumps out of folder and got scattered in root (outside the folder)

What can be the workaround ?

Besides any idea how to make life easier when integrating 2 large libraries and make sure symbols do not get overwritten… ?