Fixed not flipping the center plane blocks.

Added regression test so we'll never have to deal with it again.

src/main/java/com/sk89q/worldedit/CuboidClipboard.java

@@ -206,16 +206,16 @@ public class CuboidClipboard {
             for (int xs = 0; xs < wid; ++xs) {
                 for (int z = 0; z < length; ++z) {
                     for (int y = 0; y < height; ++y) {
-                        // Skip the center plane
-                        if (xs == width - xs - 1) {
-                            continue;
-                        }
-
                         final BaseBlock block1 = data[xs][y][z];
                         if (block1 != null) {
                             block1.flip(dir);
                         }
 
+                        // Skip the center plane
+                        if (xs == width - xs - 1) {
+                            continue;
+                        }
+
                         final BaseBlock block2 = data[width - xs - 1][y][z];
                         if (block2 != null) {
                             block2.flip(dir);
@@ -238,16 +238,16 @@ public class CuboidClipboard {
             for (int zs = 0; zs < len; ++zs) {
                 for (int x = 0; x < width; ++x) {
                     for (int y = 0; y < height; ++y) {
-                        // Skip the center plane
-                        if (zs == length - zs - 1) {
-                            continue;
-                        }
-
                         final BaseBlock block1 = data[x][y][zs];
                         if (block1 != null) {
                             block1.flip(dir);
                         }
 
+                        // Skip the center plane
+                        if (zs == length - zs - 1) {
+                            continue;
+                        }
+
                         final BaseBlock block2 = data[x][y][length - zs - 1];
                         if (block2 != null) {
                             block2.flip(dir);
@@ -270,16 +270,16 @@ public class CuboidClipboard {
             for (int ys = 0; ys < hei; ++ys) {
                 for (int x = 0; x < width; ++x) {
                     for (int z = 0; z < length; ++z) {
-                        // Skip the center plane
-                        if (ys == height - ys - 1) {
-                            continue;
-                        }
-
                         final BaseBlock block1 = data[x][ys][z];
                         if (block1 != null) {
                             block1.flip(dir);
                         }
 
+                        // Skip the center plane
+                        if (ys == height - ys - 1) {
+                            continue;
+                        }
+
                         final BaseBlock block2 = data[x][height - ys - 1][z];
                         if (block2 != null) {
                             block2.flip(dir);

src/test/java/com/sk89q/worldedit/CuboidClipboardTest.java

@@ -0,0 +1,23 @@
+package com.sk89q.worldedit;
+
+import com.sk89q.worldedit.blocks.BaseBlock;
+import com.sk89q.worldedit.blocks.BlockID;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class CuboidClipboardTest {
+    @Test
+    public void testFlipCenterPlane() throws Exception {
+        testFlip(0, 1, CuboidClipboard.FlipDirection.UP_DOWN);
+        testFlip(2, 3, CuboidClipboard.FlipDirection.NORTH_SOUTH);
+        testFlip(4, 5, CuboidClipboard.FlipDirection.WEST_EAST);
+    }
+
+    private void testFlip(int data, int expectedDataAfterFlip, CuboidClipboard.FlipDirection flipDirection) {
+        final CuboidClipboard clipboard = new CuboidClipboard(new Vector(1, 1, 1));
+        clipboard.setBlock(Vector.ZERO, new BaseBlock(BlockID.PISTON_BASE, data));
+        clipboard.flip(flipDirection);
+        assertEquals(expectedDataAfterFlip, clipboard.getBlock(Vector.ZERO).getData());
+    }
+}