Are you sure, that the problem occurs just with rs_event_post() and definitely not with rs_event_list()?
If this is the case, it would be good news, because now I can localize the bug. It is on line 914.
Please change the code as followed:
before (with bug):
$fake_secondend = mysql2date('s', gmdate('Y-m-d H:i:s', $ts_p_endtime));
$fake_secondend = $ts_p_endtime ? mysql2date('s', gmdate('Y-m-d H:i:s', $ts_p_endtime)) : 58;
And please let me know, if your problem is solved, so I can add that bugfix to version 1.3.2
Btw: The $fake_second and the "fake_sencondend just help to store or identify the information, if a starttime and/or endtime is entered or not.