Reading whiptail's manpage, I notice that the credits lists in "based on"
not only do not include its borrowing from dialog over the past 7 years,
but also omit one of the original authors.  Granted that its manpage was
originally a direct copy (changing "dialog" to "whiptail"), one would
have supposed that its maintainers would keep it up to date.

Compare with dialog's manpage...

See also
http://invisible-island.net/dialog/CHANGES

It's been also reported in Ubuntu[0] that it doesn't document the proper exit
status:

DIAGNOSTICS
       Exit status is 0 if whiptail is exited by pressing the Yes or OK but‐
       ton, and 1 if the No or Cancel button is pressed. Otherwise, if errors
       occur inside whiptail or whiptail is exited by pressing the ESC key,
       the exit status is -1.

However it's not possible for a Unix process to return exit status -1. It returns 255, as confirmed by

whiptail --yesno Wibble? 7 50; echo $?

then hit ESC.

Maybe when fixing the other issues it may be updated as well to change -1 for
255 in the man page

[0] https://bugs.launchpad.net/ubuntu/+source/newt/+bug/1010534