Hi @DennisDaniels, thanks for taking the time to report this!
Unfortunately this report lacks some information. If you have time and can still reproduce the problem, please add a more complete description to this report as text, via "Edit Task". Ideally, a list of exact and clear steps to reproduce should allow any other person to follow these steps (without having to interpret those steps) and see the same results. Problems that others can reliably reproduce can get fixed faster. Thanks!

Also, please only file one problem per report. Thanks!

I had created book A in the past
I clicked start new book
prompt says" do you want to continue book A"
book A is still there (41 pages)
I click disable book creator.
https://en.wikipedia.org/w/index.php?
title=Special:Book&bookcmd=stop_book_creator&referer=Markovnikov%27s+rule

I click start a new book
prompt says" do you want to continue book A"
I click cancel

and so on.
it's a loop

I clicked start new book

Where? Please provide a link so someone else could follow your steps (and check whether the result is the same). Otherwise we might talk about different things with different results. Thanks!

Updated with more details.

I had created book A in the past
https://en.wikipedia.org/wiki/Book:Medical_Laboratory_Basics

I clicked start new book
https://en.wikipedia.org/w/index.php?title=Special:Book&bookcmd=book_creator&referer=Main+Page

prompt says" do you want to continue book A"
I click NO
book A is still there (41 pages)

I click disable book creator.
https://en.wikipedia.org/w/index.php?
title=Special:Book&bookcmd=stop_book_creator&referer=Markovnikov%27s+rule

I click start a new book
https://en.wikipedia.org/w/index.php?title=Special:Book&bookcmd=book_creator&referer=Main+Page

prompt says" do you want to continue book A"

I click cancel

and so on.
it's a loop

thank you
Dennis