Pokemon G/S/C - Using Surf in the limit between two maps
247When Surf is used in the limit between two maps so that the player starts surfing (its sprite changes to lapras) in the tile that marks the beggining of the new map, the new map will not be loaded, and the [block data of the] current map will be loaded again instead. The connection data of the map remains, including the blocks that correspond to the strip of the connected maps, as these blocks were loaded when the old map was loaded (in this case, an area of 3x9 blocks from the left Route 27 and same from the right of Route 29).
Eventually, or possibly earlier due to the alignment of the connected maps, the X and Y coordinates will reach certain values that will make the game freeze (in this case, the Y coordinate will underflow at one point). But if you go back to the corrdinates of the original maps before, everything will be back to normal.
In reality this bug is never found obviously, so all things considered it can't be called a bug. The tile in the right of New Bark Town was hacked if you haven't noticed; it was originally a water tile (w/ ledge).