Add method for passing one BOOL. Unlike NSObject's performSelector, an NSInvocation does not make any attempt to translate arguments. It just copies from the buffer passed to addArgument:atIndex: the size of paramter specified. A BOOL is one byte (as opposed to a _Bool bool, or boolean_t which are four bytes...) so it was copying just one byte of the address of the NSNumber object and invoking it with that.

stepmania/src/archutils/Darwin/SMMainThread.h

@@ -9,6 +9,7 @@
 - (void) dealloc;
 - (void) addAction:(SEL)sel withTarget:(id)target;
 - (void) addAction:(SEL)sel withTarget:(id)target andObject:(id)object;
+- (void) addAction:(SEL)sel withTarget:(id)target andBool:(BOOL)b;
 // You must pass pointers to the objects to this method.
 - (void) addAction:(SEL)sel withTarget:(id)target andNumObjects:(int)num, ...;
 - (void) performOnMainThread;
@@ -16,6 +17,9 @@
 
 #define ADD_ACTION0(mt, t, s)    [mt addAction:@selector(s) withTarget:(t)]
 #define ADD_ACTION1(mt, t, s, o) [mt addAction:@selector(s) withTarget:(t) andObject:(o)]
+#define ADD_ACTIONb(mt, t, s, b) [mt addAction:@selector(s) withTarget:(t) andBool:(b)]
+#define ADD_ACTIONn(mt, t, s, n, ...) \
+[mt addAction:@selector(s) withTarget:(t) andNumObjects:(n), ## __VA_ARGS__]
 
 /*
  * (c) 2006 Steve Checkoway

stepmania/src/archutils/Darwin/SMMainThread.m

@@ -36,6 +36,11 @@
 	[self addAction:sel withTarget:target andNumObjects:1, &object];
 }
 
+- (void) addAction:(SEL)sel withTarget:(id)target andBool:(BOOL)b
+{
+	[self addAction:sel withTarget:target andNumObjects:1, &b];
+}
+
 - (void) addAction:(SEL)sel withTarget:(id)target andNumObjects:(int)num, ...
 {
 	NSMethodSignature *sig = [target methodSignatureForSelector:sel];