A more verbose fix to #329 and similar issues.

- Re-read chunksections the first time they're "loaded" for an operation
 - Reset the chunksection if there are block changes when setting blocks via reflection
 - These are maybe gonna affect performance a bit? Idk. Seems to be alright for me
 - These are maybe gonna make more issues? Yeah maybe, but I couldn't find any

worldedit-bukkit/src/main/java/com/boydti/fawe/bukkit/adapter/mc1_15_2/BukkitGetBlocks_1_15_2.java

@@ -221,10 +221,9 @@ public class BukkitGetBlocks_1_15_2 extends CharGetBlocks {
             if (this.sections == null) {
                 this.sections = sections.clone();
             }
-            //TODO: Understand why this causes #329, what the purpose of this is, and what may or may not break after commenting this out.
+            if (this.sections[layer] != section) {
-//            if (this.sections[layer] != section) {
+                this.sections[layer] = new ChunkSection[]{section}.clone()[0];
-//                this.sections[layer] = section;
+            }
-//            }
             this.blocks[layer] = arr;
         }
     }
@@ -299,20 +298,18 @@ public class BukkitGetBlocks_1_15_2 extends CharGetBlocks {
                     synchronized (this) {
                         synchronized (lock) {
                             lock.untilFree();
-                            ChunkSection getSection;
                             if (this.nmsChunk != nmsChunk) {
                                 this.nmsChunk = nmsChunk;
                                 this.sections = null;
                                 this.reset();
-                            } else {
+                            } else if (existingSection != getSections()[layer]) {
-                                getSection = this.getSections()[layer];
-                                if (getSection != existingSection) {
                                 this.sections[layer] = existingSection;
                                 this.reset();
+                            } else if (!Arrays.equals(update(layer, new char[4096]), load(layer))) {
+                                this.reset(layer);
                             } else if (lock.isModified()) {
                                 this.reset(layer);
                             }
-                            }
                             newSection = BukkitAdapter_1_15_2.newChunkSection(layer, this::load, setArr);
                             if (!BukkitAdapter_1_15_2.setSectionAtomic(sections, existingSection, newSection, layer)) {
                                 System.out.println("Failed to set chunk section:" + X + "," + Z + " layer: " + layer);

worldedit-core/src/main/java/com/boydti/fawe/beta/implementation/chunk/ChunkHolder.java

@@ -243,6 +243,7 @@ public class ChunkHolder<T extends Future<T>> implements IQueueChunk<T> {
         public IChunkGet get(ChunkHolder chunk) {
             chunk.getOrCreateGet();
             chunk.delegate = BOTH;
+            chunk.chunkExisting.trim(false);
             return chunk.chunkExisting;
         }
 
@@ -271,6 +272,7 @@ public class ChunkHolder<T extends Future<T>> implements IQueueChunk<T> {
         public BiomeType getBiome(ChunkHolder chunk, int x, int y, int z) {
             chunk.getOrCreateGet();
             chunk.delegate = GET;
+            chunk.chunkExisting.trim(false);
             return chunk.getBiomeType(x, y, z);
         }
 
@@ -278,6 +280,7 @@ public class ChunkHolder<T extends Future<T>> implements IQueueChunk<T> {
         public BlockState getBlock(ChunkHolder chunk, int x, int y, int z) {
             chunk.getOrCreateGet();
             chunk.delegate = GET;
+            chunk.chunkExisting.trim(false);
             return chunk.getBlock(x, y, z);
         }
 
@@ -286,6 +289,7 @@ public class ChunkHolder<T extends Future<T>> implements IQueueChunk<T> {
             int z) {
             chunk.getOrCreateGet();
             chunk.delegate = GET;
+            chunk.chunkExisting.trim(false);
             return chunk.getFullBlock(x, y, z);
         }
     };