It could be a bug. I filed a bug report too since they asked us to report "anything that breaks productivity" as well.
However, I'm pretty sure it's intentional. If you have an iPhone/iPad or whatever, look at how the icons are arranged in the quick launch bar (aka multitasking bar). They go from left to right by most recently used. If you happened to use the 4-finger gestures in the iPad developer beta, swiping left or right moves you between your apps in the same order that they are displayed in the quick launch bar. I think the idea is for OSX to mimic that behavior. If you only think of spaces as full screen apps and not desktops, you can see the similarity. That also explains why you can't "drag and drop" to rearrange spaces while in mission control. They want to OS to order them automatically.
Hopefully I'm wrong, it's a bug, or Apple gives us the option of "manual control". They can still change anything before the release. Maybe if enough people write in about it, they will.