"Back" button from custom shows causing problems

Hi. I have a PPT 2000 presentation that's 12 pages long. Off of each of those
main 12 pages is a link to a custom show, should the user choose to click
those links. On each of the custom shows is a "Back" button which will take
the user back to the page in the original main 12 page presentation from
which they left.
The problem is that when the user goes into one of the custom shows and then
uses the "back" button to get back to the main presentation. Once the user
clicks their mouse or presses the down arrow key to go to the next slide in
the main presentation (after just returning from the custom show) the next
slide that comes up is the one from the custom show from which they just
returned, not the next slide in the main presentation. How do I fix this?