I'm not able to comment on CLJ-2743 directly so I figured I would add some input here about why I think that behavior is being seen. In the JVM the catch block of a thrown exception is always stack clearing (JVMS §6.5 athrow), but at the language level Clojure presents 'try' as a simple expression which doesn't have that non-local behavior. The problem is with expressions like [1 2 (try (something) (catch Exception e 3))]. The stack frame entering into the catch is only going to be (exception) not (1, 2, exception). Essentially, the compiler needs to save the existing stack frame when it encounters a 'try' otherwise it loses those stack elements if the catch is executed. The mechanism to save these existing stack elements seemed to be to copy the entire try block into a separate function and run that. This has the benefit that the frame cleared is not the current stack frame. The downside is the synthetic closure created shadows existing symbols.