50g

I think he meant ALG instead of CAS.  Their are commands that simply don't work without using ALG mode to do them.  This is probably because the command sequence was not written in any of the many manuals HP put out.  You know the ones, that were translated from one language to the next so that they would fit inside a certain number of pages, thus saving HP the frustrating need to sell RPN calculators to actual mathematicians.  I don't think the confusion regarding CAS and ALG stem from not knowing the difference between the two, its more then likely because the Mode button is quite close to the same thing as entering into a calculator mode changing step, like you have to do in CAS.