I have the same issue. I used to be able to push and release the power button to turn the unit on. Now, I have to hold the power button in for at least 3-4 seconds. Didn't know what caused this till I found this thread. I thought the tablet was suffering from another Dell Support Technician screw up. They should post a note on the update download page that the power button will function differently after updating the bios.
Dell Consumer Support SUCKS. I should have known better than to let the non-English speaking, incompetent tech work on my tablet. He had me perform actions that I knew were not going to fix the issue I called about. At one point, the tablet became "bricked" after he did his BS and then he wanted me to send it to the depot for repair. Thanks @sshole for screwing up my tablet. It was working fine before he got his hands on it with the exception of the Bluetooth keyboard constantly loosing connection. I managed to get it up and running without his help. I finally put him on hold while I googled and found a way to get it up and running and then I found the simple solution that solved the keyboard issue.
I want to file a complaint but it will probably be a waste of time since Dell already knows the overseas support staff is subpar. Does anyone know what's the best way to file a complaint so it will not fall on deaf ears? The only complaint form I could find was on the Ireland site. Is Business Support still in the States? They were decent to work with. At least they were, years ago, when I had some business equipment under contract.