On several site I recently had 'page not found' errors for child documents within a menu structure. I tracked it down to an update made in 1.0.9, that is also present in 3.0.12. I have added comments to the particular issue:
http://tracker.modx.com/issues/9549
The snippet was altered without updating the version number, plus the alteration (from 302 redirect to 301) has the potential to break sites using FirstChildRedirect to force navigation to a child page within a container document, due to the nature of 301 redirect caching.
I would suggest having a parameter so to be able to override the redirect code for certain situations, as used in MODX Revo.
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