Don't be an idiot like me and forget to check the basics...

Question

Had to share this story of assuming a 10.6.1 update problem when it was me (I think it was anyway).
I upgraded to 10.6.1 on Thursday when I was out of the office. I have been having issues with adding attachments into Entourage (I started a topic on this last week), and I hoped they would fix it in 10.6.1. I also have a Sierra Wireless USB Modem that wasn't working that great. (The Entourage issue is still not fixed, and I haven't checked the Sierra modem yet.)
Anyway, I returned to my office Friday morning. In my office, I have a 1920x1200 Dell LCD display. So, when I take my laptop to the office, I plug in the power adapter I have there, then the display cable, the USB cable that connects to the monitor's hub (and in turn connects to my wired keyboard and printer) and the speaker mini-cable for the monitor.
I immediately discover that I cannot close the MBP lid without the machine going to sleep. On Wednesday (before the upgrade), I could keep the lid closed and the machine wouldn't sleep. I could wake it from the USB keyboard or mouse. After 10.6.1, nope. The lid had to be open to keep the machine awake. This wasn't horrible per se - the only downside was that with mirroring the built in display on my Dell display, I had to run the Dell at the laptop's screen resolution (1440x900) - so the Dell wasn't a crisp image. Not a huge problem but definitely a step back in my mind.
I tried not to work on this too much so I could focus on my actual job. But I did try a bunch of things all unsuccessfully:
1. Scoured the forums. Did find some issues with external displays and SL, but they were more related to displays not working at all. Nothing about sleep and closed lids.
2. Tweaked the energy settings to keep the machine awake, etc.
3. Even briefly tried an insomnia program to force the machine to stay awake, but that didn't seem to work either. (I didn't really want to have to run this permanently, so I deleted it pretty quickly.)
4. Tried VGA instead of DVI.
5. Tried an entirely different Dell display I happen to have (same 1920x1200 resolution, but an older model).
And then I got a battery life warning. After 4 hours, my MBP told me I was at 20% batter life. Huh? Why is the batter discharging?
Oh, idiot! On Wednesday evening, I had taken the MBP to a conference room for our fantasy football draft. Normally when I take the power supply, I just use the brick and the small adapter that fits into it. I leave the cord part plugged into the wall. But I needed the longer cord, so I took the whole thing. Apparently, when I got back to my office, I never actually plugged the cord into the wall. I just tossed it behind the desk. I didn't run the machine at work again until after the 10.6.1 install.
So, I plugged in the adapter, and lo and behold, I could now close the lid of the MBP and run the external display at its native resolution - just like the entire past month on 10.5.8, 10.6 and now 10.6.1.
Here's the part that I wonder about: Is this a change of behavior? Has OS X always required a MBP to be externally powered to run an external display with the lid closed? I don't actually know. In fact, this is now a bit of a feature for me. When I leave work at the end of a day, I usually take my laptop home. I have been manually putting the machine into sleep before disconnecting it from the power, display etc. Now, I can just disconnect it. When I pull the power, the machine automatically sleeps if the lid is closed. By the time I unplug the other connectors, the machine has finished writing out the hibernation file.
Does anyone know if this is a change?
Just thought I would share this bit of folly. I was very relieved that this issue wasn't another 10.6.1 problem. And of course a bit embarrassed. But not so much that I couldn't offer up the cautionary tale.
(And before you file this away as a rookie error, I've been using computers for 30 years, know how to program, and I manage production for a video game company. Just shows that experience doesn't always mean you are smart!)

Answer 1

Nothing to do with being smart or not. Just an oversight based on a routine getting disrupted by some new excitement. So you got to learn something new (which is wonderful about disruptions to routines), and you thankfully shared it with the rest of us.
While it's easy to say it makes sense it would have to be plugged in to operate closed, I think it's more of an afterthought of it making sense than it having to be that way. I'm sure some would complain about it not allowing you to drain the battery in that way. I like that it wants to be plugged in as it probably needs the extra boost of power anyways.
Again, thanks for sharing.