I've found a workaround for this problem. My map was meant to be rectangular 16km x 32km, but that seems to cause an issue with the grid. Once I set the extents to be 32km x 32km everything worked fine. I can turn off generation of squares I don't need, so there is a workaround at least.
Firstly, love the software, it's great fun to play with.
I'm using the latest 2.3 RC build to try and create a fairly large zone which will form the basis of my toy world. It's 16km x 32km so I can only build it in low res unless I use the grid build. My plan is to use this and Mudbox to lay out the whole region I am working on, plot out the snow / erosion, then grid it up and feed the medium res results of that into more specialised smaller machines.
I've run into what I guess is a bug however. The usual build works great and outputs the zone at 1024 x 2048 perfectly. When I go and do the tiled build however instead of outputting say 512 x 512 tiles, it outputs 53 x 16 tiles. Those aren't even powers of two, so I wouldn't expect to normally see them, let alone when I asked for something completely different.
Now, because my map is rectangular, I am only outputting some of the tiles, the right hand side in this case. Files should be 512 x 512, on an 8 x 8 grid, but they are instead 53 x 16. Tile numbering is set to 1,1.
I can probably drop back to the released version, but figured I'd post this and see if there was a solution.