In the WD, transform_tree is recursively called with:

transform_tree( x0L, y0L, x0C, y0C, x0L, y0L, log2CbSize,
    log2TrafoWidth − 1, log2TrafoHeight − 1, trafoDepth + 1, 0 )
transform_tree( x1L, y1L, x1C, y1C, x0L, y0L, log2CbSize,
    log2TrafoWidth − 1, log2TrafoHeight − 1, trafoDepth + 1, 1 )
transform_tree( x2L, y2L, x2C, y2C, x0L, y0L, log2CbSize,
    log2TrafoWidth − 1, log2TrafoHeight − 1, trafoDepth + 1, 2 )
transform_tree( x3L, y3L, x3C, y3C, x0L, y0L, log2CbSize,
    log2TrafoWidth − 1, log2TrafoHeight − 1, trafoDepth + 1, 3 )

Which mean that in the called functions, we have xBase = x0L and yBase = y0L, but these function arguments are used for chroma elements, like cbf_cb[ xBase ][ yBase ][ trafoDepth − 1 ], so we should have xBase = x0C and yBase = y0C, and the recursive calls should be changed to:

transform_tree( x0L, y0L, x0C, y0C, x0C, y0C, log2CbSize,
    log2TrafoWidth − 1, log2TrafoHeight − 1, trafoDepth + 1, 0 )
transform_tree( x1L, y1L, x1C, y1C, x0C, y0C, log2CbSize,
    log2TrafoWidth − 1, log2TrafoHeight − 1, trafoDepth + 1, 1 )
transform_tree( x2L, y2L, x2C, y2C, x0C, y0C, log2CbSize,
    log2TrafoWidth − 1, log2TrafoHeight − 1, trafoDepth + 1, 2 )
transform_tree( x3L, y3L, x3C, y3C, x0C, y0C, log2CbSize,
    log2TrafoWidth − 1, log2TrafoHeight − 1, trafoDepth + 1, 3 )