Add a between-instructions enforcement of SH = 1.

Processors/65816/Implementation/65816Implementation.hpp

@@ -67,6 +67,9 @@ template <typename BusHandler, bool uses_ready_line> void Processor<BusHandler,
 					last_operation_pc_ = registers_.pc;
 					last_operation_program_bank_ = uint8_t(registers_.program_bank >> 16);
 					memory_lock_ = false;
+
+					// Reenforce the top byte of S if applicable.
+					registers_.s.halves.high = stack_address();
 				} continue;
 
 				case OperationDecode: {

Processors/65816/Implementation/65816Storage.cpp

@@ -1131,11 +1131,10 @@ void ProcessorStorage::set_emulation_mode(bool enabled) {
 		set_m_x_flags(true, true);
 		registers_.e_masks[0] = 0xff00;
 		registers_.e_masks[1] = 0x00ff;
+		registers_.s.halves.high = 1;
 	} else {
 		registers_.e_masks[0] = 0x0000;
 		registers_.e_masks[1] = 0xffff;
-		registers_.s.halves.high = 1;	// To pretend it was 1 all along; this implementation actually ignores
-										// the top byte while in emulation mode.
 	}
 }