Back in the day (get off my lawn!) once a piece was uploaded it was committed. Occasionally, if you had an upload page cached in your browser you could re-up a square, but you couldn't count on it.

Now, I do use the re-up "feature" from time to time myself, to fix a minor mistake or add a new idea that I missed in my initial rush of pixel excitement. It's definitely got some pros. But feel that, in general, once someone has added an adjoining square, yours should be fixed in its current state.