Thanks for the issue report, I can understand the concern.
I can tell you that we know that there are "Href" values on every page we host that use URL parameters to take a specific action. For example, and Href ending in /notification in the link you reference below is in fact a button that sends a RESTful API request to subscribe the logged in user to receive notifications about that topic.
So, I can agree with you that there are strings that seem to be links on our page that in fact are not links a customer would ever see or be prompted to navigate to. Because they are not backed in webpages, many site management tools flag them as giving a 404.
Now, for the good news. The official Google Webmaster blog has quite a bit of advice about 404s on this page:
Therefore, we do not experience an SEO penalty from these href values. In fact, by using a CNAME, you should expect to have the SEO improvement of incorporating many pages of customer-generated, truly unique content that will improve the domain's standing overall.
Finally, I wanted to let you know that we are looking at doing a rewrite of the platform over time that I expect will greatly reduce the number of such links on our pages.
Now, one point of clarification. The tag "new" sounds like it would fit into the above category. Do you know if any other tags show this 404 behavior?
Thanks in advance for that information.