Any WYSIWYG edit to a WYSIWYG zone (defined using the WYSIWYG plugin) fails quietly if the call to the plugin follows an inclusion (made using the INCLUDE plugin). CKEditor goes away as expected and the contents of the zone are displayed, but instead of the new contents, the old content shows.
This bug exists in Tiki 12 and persists in trunk as of r64360.
If wiki page Parent includes page Child, the following WYSIWYG zone causes the wysiwygPlugin() function to be called at page load with its page parameter set to "Child" instead of "Parent" as should be the case. Which causes the AJAX calls to action_replace() from edits to have the wrong value for their page parameter, causing them to have no effect, and action_replace() to return simply "".
wysiwygPlugin's parameter is wrong because wikiplugin_wysiwyg()'s $sourcepage variable has the wrong value, because it is wrongly set to $wikiplugin_included_page instead of $page. This is due to a parser context management issue.
The part about error reporting was fixed in the following commits.
The patch attached is an actual fix, but is against Tiki 15, and relies on considerable parser changes which are not in the Tiki community's repositories (see thread "Parsing context and inclusions").