I don't have any problems with mine either on the latest firmware. My S1 is a revision 1.5.
It may behoove everyone on the thread if the guys having problems (and the ones that don't) with the new firmware list their board revision numbers. It could be specific to older S1s.
I tried it on a v1.5 with problems - didn't try it on anything else after that
My original AntMiner, cgminer runs CPU 99/100% ...
It says: cgminer 3.4.3-1
I am running the latest firmware on early and late ant's, and do not have any problems, nor do I get any reboots, he CPU is maxed on the last two firmware releases running cgminer but it still does the job even if the web interface is slow and hash rate at the pool is unchanged.
What I have found is that the instance of cgminer is very sensitive to network and power problems, it causes all manner of issues.
You must set up the all the network correctly, LAN, WAN and WWAN or the cgminer process spends a lot of it 3 minutes of life waiting to be killed and restarted by the daemon.
Power is also problematic, it needs clean uninterrupted power to keep the error rates down, 'X's to a minimum, and stop weird reboots. I can get ant's to run on some power supplies at low wattage then move the connectors to the end of a cable and experience higher error rates, 'X's and reboots. What I have found is that the better power supplies are simply better.