Currently the "Get Size from Library" checkbox is stored as a local parameter in each forest object, is not a global switch. You are right, this can be a bit annoying, we will study to save the last used value as default.
About the library, we are making a complete rewrite of the library system to support mesh objects, a better file organization and new features. Because that the current beta don't includes the latest fixes in the library (as the gamma issue). We will include the new system in the next betas.
Some features are open for now, any idea or wishlist about libraries will be welcome.