I finally figured out what was triggering the weird behaviour where everything that was sent to the APL interpreter was echoed to the screen.
The problem happens when readline_lib::add_history is called when Readline is disabled.
The following patch will fix this:
===================================================================
--- Input.cc (revision 56)
+++ Input.cc (working copy)
@@ -255,7 +255,7 @@
{
while (*l && *l <= ' ') ++l; // skip leading whitespace
- if (*l) readline_lib::add_history(line);
+ if (use_readline && *l) readline_lib::add_history(line);
}
return l;