The above question was solved by Måns in the following thread on the TiddlyWiki google group...
search for: "saving checked html form checkboxes in a tiddler?" or try this link, which should hopefully take you there, if you have already joined that group: https://groups.google.com/forum/#!topic/tiddlywiki/E22oIEryiPo -- You received this message because you are subscribed to the Google Groups "GTD TiddlyWiki" group. To view this discussion on the web visit https://groups.google.com/d/msg/gtd-tiddlywiki/-/j22tsLV3F_4J. To post to this group, send email to gtd-tiddlyw...@googlegroups.com. To unsubscribe from this group, send email to gtd-tiddlywiki+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/gtd-tiddlywiki?hl=en.