I updated my iPad 1 with the new operating system (5.1) and now my passcode option doesn't work, doesn't ask for passcode now with passcode turned on in settings. The only way passcode works is if I actually power down the iPad, doesn't work when ipad goes in sleep mode. With the old OS it would always ask for passcode, both on power down and sleep mode. Is this some new quirk of the new operating system? Or am I overlooking something?

try changing the passcode and then turning it off and back on.

Here's how I got it to work, went to "passcode lock" (which was ON), entered passcode and new menu came up and had to toggle on "immediately", powered down unit, powered up and it seems to be working OK now.