...Yes I am updating to 819 soon! :P
Anyway, Whenever I go to the tile editor and copy paste some stuff around I always get some garbage appearing in the top-right corner:

I don't think there is any special rare formula to trigger this, as it happens consistantly. (I'm using 8-bit tiles, not sure if that why)
Very minor, doesn't corrupt anything.
...hrm...: Is small mode being phased out completely? ..I'f so I'll just switch over to large mode and stop posting the bugs with small.