sbolel:
Whenever another electronic that puts a heavy load on the circuit is plugged into the same socket as the arduino, something happens and the arduino stalls and/or loses power. This also prevents the watchdog reset from executing somehow...
My question is: how can I prevent / safeguard against this?
...
And why is the board not resetting when it doesnt get a wd_reset() after 8 seconds?
I am having the same problem in my apartment. I have found that whenever I rapidly turn on and off the air compressor, after about 20 toggles, the Arduino Duemilanove will halt. My Arduino is plugged into the same outlet as the fridge and when I unplug and replug the fridge, the Arduino halts after about 2-6 toggles, so it is obviously a power issue.
When I say Arduino Duemilanove "halts", it resets and then does not even execute its setup function. I used some LEDs to verify this, then I eventually used another Arduino to monitor the first with the same results. This is what you are experiencing with the WDT not being turned on. The funny thing is that the second Arduino does not crash, only the first, so it has to do something with my code.
I believe the workaround is to turn on the WDTON fuse with an ISP programmer. That way you don't need to enable the WDT in software.