Opening the source target of an annotation doesn't take me to the epubjs reader.
per https://github.com/futurepress/epub.js/issues/64
@kathi-fletcher created this annotation: https://hypothes.is/a/A-EMAlnGRZioyH3rtDbreA
Which points to this page: http://oerpub.github.io/epubjsreader-demo-book/content/m45983.xhtml
But following that page doesn't invoke the epubjs reader. Instead I just get a representation in HTML/XHTML of that text.
We need target URLs that invoke the epub reader when they're followed.
Hypothes.is currently uses the URL and (if available) rel="canonical".
I'm not sure how much has changed in the last several months (likely lots!), but it looks like URLs now are set with the newer HTML5 API's, so Hypothes.is could watch for those changes and use those URLs for adding / removing during page navigation--hopefully!