When using the testfor command on a realm, such as "testfor @a[x=1, y=5, z=1, r=1]", instead of behaving as intended, it instead changes the command input to "################################################" when leaving the command block UI.

It works as intended in singleplayer worlds and breaks with @a, @e, @r, @p, and player names and breaks with any of the 3 kinds of command blocks.