I have found that Energy Dimmer 2.13 will reset the Treo 650 if auto-off turns off the screen while loading a page. I have already sent an e-mail to the developer reporting this bug:

I found a bug on dimmer 2.13 while using Blazer on the Treo 650. The problem is when Blazer is downloading a page and Auto-Off turns off the screen it causes the PDA to reboot. Could you please fix this bug? Maybe disable auto-off when there is network traffic.

In the mean time, make sure you set up auto-off to something greater than 3 minutes or so.