Ehm, what the hell is this?

Please have a look at this screenshot. Look at the y-coordinate. I could probably go higher, at some point it just doesnt make sense anymore. I'm running a pretty vanilla craftbukkit 1.2.5-r4 server with essentials, rpermissions and portals. I have no idea since when this is possible, or if this might even be a feature. Right now I'm thinking this is just a bug and I'll construct a tower to test the theory that I'm not actually this high. But still. wtf.

http://imgur.com/zfuBO

edit: I just let myself fall from the height, and it took a good 30 seconds, way longer than it'd take from 256. So yeah. Gonna test if I can actually build up there.

edit2: okay, I can only build to 256. So this is just a case of me not being familiar with the fly command? -.-

 

I don't believe the Y-Coordinate goes any higher, as it doesn't need to count up there anymore.
Although with the SS you provided it shows it went much higher, I'm rather confused.

 

Actually, you can go exceptionally high.