Well, I can certainly see how it would be useful in certain situations. However, since Filemaker makes a big deal about it in their documentation, I wouldn't file this under "undocumented feature", but rather full-fledged bug. I realize that they can't control how browsers are built, but since they make such a big deal about security and being sure that users are logged off, they could have a) come up with a solution or : Emphatically stated that none of this will work without closing the browser.
*shrug* Thankfully I almost never use IWP. This is a quick project for a client on a very small budget.