For those of you who haven't noticed yet, there is a classroom random event which RSBOT can not currently solve. I think that holding a Book of Knowledge would possibly prevent you from having another classroom random as long as you hold it.
my cousin had 4 lamps and 4 books in his invent while going for 85 mining. i was like why u want them? and he said it would look cool for his video. =P so yeah they stack