I was playing on 1.8pre2 and everything went normally until I slept in a bed outside in the middle of the night

It became daytime but mobs kept spawning (and the undead instantly caught fire as expected). At first I thought they were left over from the nighttime but as I killed them more and more kept coming until I began to be overrun. They were clearly spawning in the daytime as there was no cave or adequate shade nearby.

Run 1.8pre2 on a computer with Windows 8, create a new survival world, stand in the middle of a field (with horses) in the nighttime, sleep in a bed, then see if mobs continue to spawn.