Python 2.5 Modules/readline.c line 681 is:

	return completion_matches(text, *on_completion);

on_completion is a function declared as:

static char *on_completion(char *text, int state);

completion_matches is a macro that expands to: 

rl_completion_matches((x), ((rl_compentry_func_t *)(y)))

SO, the second parameter to completion_matches should be a function pointer (on_completion), not the dereferenced function pointer that is currently passed to it (*on_completion).

Can you please provide a patch that fixes things?  It's difficult for us to provide a patch that will fix the problem on AIX because we don't have access to an AIX machine for testing.

I'll close this on lack of feedback unless someone voices opposition.