What causes the Documentation stack to fail?

[Mikey]

I can regularly make the Documentation stack fail to show items that
I'm searching for, but I don't understand what causes it.  For
example, I was messing around with a stack this afternoon, and I
wanted to check something out about the substacks property.  So I went
to the documentation stack, and typed in "substack" in the filter
dialog.  The list was reduced, but the substacks property detail was
never displayed.  I had to quit RR in order to fix the problem.  After
several iterations I'm completely baffled.
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On the first day, God created the heavens and the Earth
On the second day, God created the oceans.
On the third day, God put the animals on hold for a few hours,
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And God said, "This is good."