Flymod destroys your maps

[Wire-xx]

As you maybe noticed, flying around with Zombe's flymod everybody is able to make your map really much bigger. That leads into horrible laggs, because the server creates every single Chunk when flying into a new region. Some people expanded my map from 200 MB to 400 MB in 5 Minutes!
I know that this is not a hMod issue, and that Notch should fix coordinate checking for smp server, BUT PLEASE can you write a fix for it, so players get maybe kicked if they are above the ground? It would be soo helpful if this function would exist (maybe on/off in server properties)