Ajax issue with $page_array option - Warning: Invalid argument supplied for foreach() in element_children() (line 6590 of common.inc

When employing ajax forms, if the Devel option "Display $page array" is active - the ajax portion appended contains many render errors from core with this message:

Warning: Invalid argument supplied for foreach() in element_children() ... line 6590 of common.inc

I'm posting this mostly so those who google the error directly can find this page, as this might help - the issue is not a major one.

This occurs especially with users who do not have devel permission. Somehow giving anonymous users devel access seems to make this go away.

Simply turning off the devel option of display $page array when you're working on your ajax forms seems to do the trick here.