Saving works here (just modified some tiles), but when trying to test the result with the settings you mentioned in the doc (A1200 non expanded, folder mounted as CD0) I get :
Program failed (error #8000006)
Besides that the editor looks really good
I bet gimbal will like it aswell
Edit : If I try to add a template after 44 it won't let me. Just nothing happens.
Edit 2 : Could there be a 'clear level' option? You know, to design stuff from scratch