diff --git a/worldedit-core/src/main/java/com/sk89q/worldedit/EditSession.java b/worldedit-core/src/main/java/com/sk89q/worldedit/EditSession.java
index 37dd8ea24..8f780c36a 100644
--- a/worldedit-core/src/main/java/com/sk89q/worldedit/EditSession.java
+++ b/worldedit-core/src/main/java/com/sk89q/worldedit/EditSession.java
@@ -1118,7 +1118,7 @@ public class EditSession extends PassthroughExtent implements AutoCloseable {
                 new RegionMask(new EllipsoidRegion(null, origin, Vector3.at(radius, radius, radius))),
                 new BoundedHeightMask(
                         Math.max(origin.getBlockY() - depth + 1, getMinimumPoint().getBlockY()),
-                        Math.min(getMaximumPoint().getBlockY(), origin.getBlockY())),
+                        Math.min(getMaxY(), origin.getBlockY())),
                 Masks.negate(new ExistingBlockMask(this)));
 
         // Want to replace blocks
diff --git a/worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BlockMask.java b/worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BlockMask.java
index c36c5fb82..a0b67290f 100644
--- a/worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BlockMask.java
+++ b/worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BlockMask.java
@@ -180,12 +180,22 @@ public class BlockMask extends ABlockMask {
     public Mask tryCombine(Mask mask) {
         if (mask instanceof ABlockMask) {
             ABlockMask other = (ABlockMask) mask;
+            boolean modified = false;
+            boolean hasAny = false;
             for (int i = 0; i < ordinals.length; i++) {
                 if (ordinals[i]) {
-                    ordinals[i] = other.test(BlockState.getFromOrdinal(i));
+                    boolean result = other.test(BlockState.getFromOrdinal(i));
+                    hasAny |= result;
+                    modified |= !result;
+                    ordinals[i] = result;
                 }
             }
-            return this;
+            if (modified) {
+                if (!hasAny) {
+                    return Masks.alwaysFalse();
+                }
+                return this;
+            }
         }
         return null;
     }
@@ -194,12 +204,17 @@ public class BlockMask extends ABlockMask {
     public Mask tryOr(Mask mask) {
         if (mask instanceof ABlockMask) {
             ABlockMask other = (ABlockMask) mask;
+            boolean modified = false;
             for (int i = 0; i < ordinals.length; i++) {
                 if (!ordinals[i]) {
-                    ordinals[i] = other.test(BlockState.getFromOrdinal(i));
+                    boolean result = other.test(BlockState.getFromOrdinal(i));
+                    modified |= result;
+                    ordinals[i] = result;
                 }
             }
-            return this;
+            if (modified) {
+                return this;
+            }
         }
         return null;
     }
diff --git a/worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/MaskIntersection.java b/worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/MaskIntersection.java
index 751ee073b..d7743c520 100644
--- a/worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/MaskIntersection.java
+++ b/worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/MaskIntersection.java
@@ -144,10 +144,10 @@ public class MaskIntersection extends AbstractMask {
         Set<Map.Entry<Mask, Mask>> failedCombines = new HashSet<>();
         // Combine the masks
         boolean changed = false;
-        while (changed |= combineMasks(pairingFunction(), failedCombines));
+        while (combineMasks(pairingFunction(), failedCombines)) changed = true;
         // Optimize / combine
         do changed |= optimizeMasks(optimized);
-        while (changed |= combineMasks(pairingFunction(), failedCombines) && --maxIteration > 0);
+        while (combineMasks(pairingFunction(), failedCombines) && --maxIteration > 0);
 
         if (maxIteration == 0) {
             getLogger(MaskIntersection.class).debug("Failed optimize MaskIntersection");
@@ -169,6 +169,7 @@ public class MaskIntersection extends AbstractMask {
             outer:
             for (Mask mask : masks) {
                 for (Mask other : masks) {
+                    if (mask == other) continue;
                     AbstractMap.SimpleEntry<Mask, Mask> pair = new AbstractMap.SimpleEntry<>(mask, other);
                     if (failedCombines.contains(pair)) continue;
                     Mask combined = pairing.apply(pair);