Even though by the time I apply my configuration changes and everything looks valid (i.e., I get the OK), running the job gives me the following output:

[confluence] Unable to locate page: JENKINS/Release+Notes+Test+Page.
[confluence] Check that the page still exists. If the Space and/or Page name contain build-time parameters, check that the parameter(s) are set to the proper value(s).

Where my full URL is something like http://confluence/display/JENKINS/Release+Notes+Test+Page

If I change the Page name to ReleaseNotesTestPage everything is published okay:

[confluence] Uploading attachments to Confluence page: http://confluence/display/JENKINS/ReleaseNotesTestPage
[confluence] Uploading 0 file(s) to Confluence...
[confluence] Done
[confluence] Performing wiki edits: Append content