[TYPO3] page jumps to another page

[Bing Du]

Hi,

I've seen this problem once on Typo3 V3.8.1.  Today, we upgraded to
V4.0.2.  I saw the problem with another page again.

Opportunities
   blah
   blah
Extension and Outreach
Resources

The Resources page is just a regular standard page and has its own
content.  It's not hidden.  It's not a link or shortcut.  But for some
reason, when you click 'Resources', the 'Opportunities' menu expands and
the 'Opportunities' page shows up.  I've checked the 'Edit page header' of
the 'Resources' page but don't see anything that could redirect
'Resources' to 'Opportunities'.  The 'Opportunities' page is also a
standard unhidden page.  Has anybody else seen such a weirdness?  Thanks
in advance.

Bing