Perhaps you have a Retry on failure in the On error tab? Or use some kind of Condition? The log should probably reveal this.
No retry on failure configured.
No conditions are enabled.
I can't tell from looking at the log. I've attached the relevant portion. One thing strange, if see how the time counts up to 6:00:27 AM, and then backs up to 5:59:54. What the heck is that all about?
Even the run missed jobs query looks wrong (end time is before the start time):
7/8/2013 6:00:10 AM Info Running missed jobs between 7/8/2013 6:00:22 AM and 7/8/2013 6:00:10 AM
Also, we've changed nothing on this machine, other than the change to the service logon user.