One often overlooked issue of IAP is that it is In Application Programming. Thus the ROM code called assume that a reset follows. For that reason the code (at least those I know of) use DATA storage and the stack 'as it wants to'. Thus those that use IAP for things other than actual programming with a reset to follow are in for some nasty surprises. What does work is the following: move all DATA (20-ff) to XDATA, set the stack pointer to 80, do the 'IAP which is not programming' and restore DATA.

Erik