Running version 2.3.5.8 there's a change in the functionality as described on this page: http://www.mojoportal.com/same-content-on-all-pages.aspx
Hard coding a module:
Example: <portal:ModuleWrapper ID="mdl33" runat="server" ConfigureModuleID="33" />
If you hard code a module into your layout.master page (as I often do) you used to be able to edit that module content from any page simply by clicking the "edit" link as normal. Current version if you try and edit you are taken to an AccessDenied.aspx page instead (regardless of the permissions on the module). You can still edit the module settings from any page, but can't actually edit the content (in this case HTML module).
I'm not sure which version of MP caused this change in behavior but on sites of mine where this used to work it now doesn't. The only way to edit the module is to place it on a page and then edit it from the page where it actually lives (or edit from content. This isn't ideal, it's often nice to have a shared module that's on all pages for news/callouts/etc and if the client can simple edit that module as usual that seems the simplest.
Note: modules also can't be edited via the "content manager" (ContentCatalog.aspx) which really leads me to believe this is a bug and not by design.