This is an old revision of the document!
Bitsy Bye, as included with ProDOS 2.4.0 and 2.4.1, accidentally access $C029, switching out the main ROM bank. This causes a crash when it tries to use a firmware routine.
A fixed version of 2.4.1 is available on this page.
Two parts of the program access $C029 without checking to see if the machine is a IIgs or not.