At the REPL, I accidentally typed:
user=> 1. "\w+"
RuntimeException Unsupported escape character: \w clojure.lang.Util.runtimeExce
You can see the confusing result (the REPL is also left in an unclosed string). After looking at LispReader.java, it seems to me DispatchReader ought to at least check for whitespace before calling CtorReader (perhaps better would be to check for a valid symbol character).