I've ran across two bugs in this plugin that I've fixed.
The first is related to showing the custom blocks on post/page edits. For some users, the blocks never appeared. It's related to the context not being used properly...
function add_post_metadata_group() I modified the meta_box call to use the $group->context value, and not the hard-coded one. Same thing also in add_options_metadata_group().
Second is the tinymce editor was being initted twice on a page ... found to be caused by the function admin_head() calling wp_tiny_mce(). Commenting this line fixed the problem.