ParametricCallable.mayConsumeArguments() handles flags better.

src/main/java/com/sk89q/worldedit/util/command/parametric/ParametricCallable.java

@@ -345,7 +345,10 @@ class ParametricCallable implements CommandCallable {
         //     - Before required parameters: Consume if there are 'left over' args
         //     - At the end: Always consumes
 
-        if (parameter.isOptional() && parameter.getFlag() == null) {
+        if (parameter.isOptional()) {
+            if (parameter.getFlag() != null) {
+                return !parameter.isValueFlag() || context.hasFlag(parameter.getFlag());
+            } else {
                 int numberFree = context.argsLength() - scoped.position();
                 for (int j = i; j < parameters.length; j++) {
                     if (parameters[j].isNonFlagConsumer() && !parameters[j].isOptional()) {
@@ -360,6 +363,7 @@ class ParametricCallable implements CommandCallable {
                     return false;
                 }
             }
+        }
         
         return true;
     }