Hi thanks for the update!
A few comments...
The cursor co-ordinates is a nice improvement, thanks! But, I don't think it needs to be THAT exact. For example, your editor goes as far as two decimal places (e.g. 27.84) but I think one decimal place (e.g. 27.8) is more than sufficient.
The little yellow square inside the white box for cursor co-ordinates is useful but maybe it might be more useful if it "snaps" to different positions, like it does when moving from one cube to another? Snapping to a 10x10 grid inside the cube would be useful.
When you have cursor co-ordinates on and you enter zone editor, the little yellow square defaults to the middle of the cube. Do you think once you enter zone editor the cursor co-ordinates is disabled (then re-enabled once zone editor is closed)?
Also, with the cursor co-ordinates enabled, you can move your mouse and each cube is highlighted by a white outline? That is fine, but you can left-click and it selects or de-selects cubes. Any reason for this?
The CPU usage when cursor co-ordinates is pretty high! When minimised the program uses 0-3% CPU (as before), when not minimised and NOT using the cursor co-ordinates it is about 25-27% but when you are using it it goes up to 52-54%!
On the File > Open menu why does it come up with MMP files first? Surely it should be GMP?
When opening a map that doesn't have an MMP file, why does it default to the last MIS file used, or if it can't do that, why use the first alphabetical MIS file?
When loading a map with no associated MMP file and then you try and load a MIS file the editor crashes! I did load GMP first, then load STY then MIS and then it crashed completely, didn't even get a chance to load the map! As stated, this does not happen if you load an MMP file first.
Sorry if the above sounds negative but I don't mean it that way! Just trying to help improve it
I'll keep playing with it and report back when I have more information.