The P8 library is quite quirky, dare I say buggy, under Mac OS 10.5 and 10.6, even after SR1. The library function buttons on the bottom can vanish at seemingly random intervals, though they can usually be reacquired by going into another category and back again. For me, rendering doesn't seem to have anything to do with it.

Adding an item to the library won't show up there until you go out and into that category again. Sometimes you have to select the category again to make sure you are still there (the library forgets where you are and may not save the item even though it goes through the steps without complaint). This is heartbreaker if you close P8 without saving, thinking you have put your in the library but actually haven't. 

I don't know how much of this is due to the fact that the library is now Flash-driven and no longer constantly polls the drive (which I suppose is the reason for the refresh buttons). BBill could answer this more intelligently.