MZ3 Help window at start-up missing

If you wonder why sometimes that window is visible and then disappears for long times... here the simple answer: It is a feature and not a bug ;-)

You can configure the behavior in setting the book@openhelp parameter, as explained in the Wiki

openhelp="once"      the default
openhelp="always"
openhelp="never"

If set to once (which is the case if you do not explicitely set that parameter differently) that help window only shows up the very first time when the book opens. The "already visited once - flag" is saved in the Flash cache, and therefore remains set forever. Also clearing the browser cache does not reset that flag!
If you want to be on the safe side, you can add help information to the pagebackground or set openhelp to always.