Thanks for the bug report; I installed the attached to fix it. The problem with 
your test case was neither C stack overflow nor failure to unwind the Lisp 
stack: it was failure to restore the Lisp evaluation depth (which is a separate 
thing from the Lisp stack size).

By the way, why are there two different limits? That slows the interpreter down 
a bit.  Why don't we simply have a limit for the Lisp stack size? Every time 
lisp_eval_depth grows, the stack size grows, so limiting the stack limits the 
evaluation depth for free. If we had done things this way, the interpreter would 
be a bit faster and this bug would never have occurred.