Well, it's not exactly a bug per say, but in the 'void DrawTile' section, it says this:
void DrawTile(int layer, int x, int y, int tile, int blockw, int blockh,
int cset, float scale, int rx, int ry, int rangle,
int flip, bool transparency, int opacity)
* Draws a block of tiles on the specified layer of the current screen,
* starting at (x,y), using the specified cset.
* Starting with the specified tile, this method copies a block of size
* blockh x blockw from the tile sheet to the screen. This method's
* behavior is undefined unless 1 <= blockh, blockw <= 20.
* The scaling and rotation parameters are reserved for the future, and
* not currently implemented. This method's behavior is undefined unless
* rx=ry=rangle=0 and scale=1.
* Flip specifies how the tiles should be flipped when drawn:
* 0: No flip
* 1: Vertical flip
* 2: Horizontal flip
* 3: Both (180 degree rotation)
* If transparency is true, the tiles' transparent regions will be
* respected.
* Opacity controls how transparent the solid portions of the tiles will
* be. Values other than 128 (solid) and 64 (translucent) are currently
* undefined.Here it is stated that a flip value of 1 is vertical and 2 is horizontal, where infact a value of 1 is horizontal and 2 is vertical.
Oh, and the message when you first open the new beta says 'Warning this is beta' rather than 'Warning this is a beta'