While the /> syntax is inherited from HTML tags, aren’t TiddlyWiki widgets wikitext code that gets parsed by the TiddlyWiki core? Isn’t it fair to expect to see an error message on screen in such situations? Of course the most useful scenario would be having more verbose error messages in filter expressions, to prevent the common misuse of misc "pesky brackets"™
By leaving the widget unclosed, TW considers everything after the first widget instance as “within the body” of that widget, until the end of the tiddler when any open widgets are automatically closed. So, everything after is ignored, not just additional images.
I agree that the fact that obvious mistakes are silently swallowed in cases like this isn’t great, but it seems completely in line with how HTML works, so I don’t think I blame TiddlyWiki for this one.
Perhaps there could be a case for a “strict mode” – but then we basically tried that with XHTML and apparently nobody liked it.