I've used editor a few times. To find a way through one maze, then the case I described, then to find the way in the looping screen of * ending (I have been near the dude that tells about the pillar, but missed him), to find ending 6 and also found some other hidden places.
Another situation where you have to restart is the * ending.
When you fall through the black tower at the end, after the words are scrolling but before you reset to the first fall through the world, you can grab the wall and climb up and be at the beginning of the level again but with the ability to climb.
But if you don't grab the wall and fall, there's a nasty autosave shift in x988y997 that would take away the opportunity. There are some other autosave shifts that I don't like, like one in x1022y975, it did a bad thing for me once. Overall I don't see a reason for such autosave shifts, save points are always better.
Some small bugs:
x1009y994 - wallswim if you go up.
x1034y954 - you can fall down into a void screen.
x1034y952 - you can climb up into a void screen.
x1040y957/x1040y958 - wallswims at x3 and x21.
x1026y964 - if you jump in the next screen when you fall down you'll find yourself in void screens. There are also void screens to the right and left of x986y975.
x1015y992 - wallswim shift.