fmgr_info_cxt_security() screwing memory ?

Hi, I'm calling an arbitrary user-defined function from the backend. 
Although I can do it via FunctionCallInvoke, I have a weird problem when 
calling fmgr_info. The call results in a argument variable (eventType) 
being cleared. A gdb hardware watch says that the variable is modified by 
fmgr_info_cxt_security (fmgr.c:185): "finfo->fn_extra = NULL"; Any ideas of 
what is happening?

For simplicity, in the following snippet I have hardcoded foid to some
(PGPSQL) function id and removed the rest of the call-related statements.

static void execEventTypeFunc(char *eventType, Oid funcId)
{        FmgrInfo *finfo;        FunctionCallInfoData fcinfo;        Datum           result;        Oid foid = 17283;
        finfo = (FmgrInfo *) palloc0(sizeof(FmgrInfo));
        fmgr_info(foid, finfo);
        ...
}

Thanks,

Luis Vargas