Hello - I have filed a bug report at http://code.google.com/p/semanticpageseries/issues/detail?id=1&thanks=1&ts=1329252765 because MW Bugzilla doesn't have an entry for SPS - is this the right place (I'd prefer MW Bugzilla though).
Topic on Extension talk:Semantic Page Series
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Thanks for the report, I will fix the bug next week. For the time being you can either revert to SF 2.4 (release version) or replace all calls to SFFormUtils::hiddenFieldHTML by Html::hidden. Calling unhandledFieldsHTML can not work, the functionality is different from hiddenFieldHtml.
I also added contact information to the Extension Page.
Ok, just checked the fix in. There was also a bug in SF that is fixed now. If you update both extensions to the latest dev version, it should work.
Cheers,