The cljs.analyzer/type-check-induced-tag function looks for code that applies instance? or implements? to a couple arguments.
In the case that the first argument is a special, it can skip further processing. In particular this would avoid attempting to analyze ., in a form that looks like
and therefore avoid issues surrounding and in particular, this comment https://clojure.atlassian.net/browse/CLJS-712?focusedCommentId=47541&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-47541