This is a follow on from #680026: Custom Breadcrumbs doesn't work if view is provided a default argument - not a dupe because this is about tabbed views, not default arguments. post #4 in that issue raised the same problem though.
The issue is:
Custom Breadcrumbs works great on the views with tabs when one goes to the view URLs, but not when going to the default tab page. E.g.
/myview/othertab are fine, but the default page at
/myview has no custom breadcrumbs.