Mysterious std::list::size() mismatch - c++

Question

I've got a "list iterator not dereferencable" error. I've figured that this is often caused by trying to iterate too far through a list, however I can't find the cause of it. I'm staying strictly within the functions of the std::list API, so I don't know what exactly is going wrong in the below code to cause this error.
There are a few mysteries surrounding the error. The main focus of this issue is GameStateManager::HandleEvents(), during the list iteration. At the point of breaking, I have added five elements to the list, called list::remove() for each (making an empty list) and added four more elements. However, as you can see below, I print the size of the list before iterating through it. While debugging, this has shown something confusing - the size, as returned by list::size(), is different from the actual size (as viewed in the list::size variable itself, via the Visual Studio debugger). This only happens prior to the error - normally both values are the same. However, right before the error, size() returns a value unequal to the size member value of the list. It consistently contains the previous value, prior to the first elements being removed. I can't help but feel this discrepancy has something to do with the "list iterator not dereferencable" error.
Additionally confusing, the print command is not executable immediately prior to the error-triggering code. Additionally, in GameStateManager::HandleEvents(), no custom breakpoints are triggered prior to fatal for loop. Perhaps these anomalies are separate issues, however I figured they may be useful to know.
GameStateManager.h
#pragma once
#include "Tools.h"
#include "TitleScreenState.h"
#include "Game.h"
#include "Timer.h"
#include <list>
class GameState;
class EventHandler;
class GameStateManager
{
public:
GameStateManager(void);
~GameStateManager(void) { m_currentState->OnEnd(); }
void Run(void);
void Quit(void) { m_running = false; }
// Event Handler Functions
void AddHandler(EventHandler* handler) { m_eventHandlers.emplace_back(handler); }
void RemoveHandler(EventHandler* handler) { m_eventHandlers.remove(handler); }
private:
std::list<EventHandler*> m_eventHandlers; // All of the handlers who are passed the events
bool m_running; // The universal boolean for whether or not the program is running
int delta; // The time since the last frame
Timer m_FPSTimer; // The timer that keeps track of the time since the last update
GameStateID startStateID;
GameState* m_currentState; // Pointer to the current game state
// Poll and pass events to the current state
void HandleEvents(void);
};
GameStateManager.cpp
#include "GameStateManager.h"
#include "EventHandler.h"
#include "ToolKit.h"
#include "Game.h"
#include <time.h>
GameStateManager* g_manager = nullptr;
GameStateManager::GameStateManager(void)
: m_eventHandlers(), delta(0), m_running(true), startStateID(GSID_TITLE),
m_currentState(nullptr), m_titleScreen(nullptr), m_game(nullptr)
{
// Initialise time
srand(time(nullptr));
}
void GameStateManager::Run(void)
{
Initialise();
while (m_running)
{
// State's key press responses
m_currentState->OnKeys(SDL_GetKeyboardState(nullptr));
// Update State
m_currentState->OnUpdate(delta);
// Render State
m_currentState->OnRender();
HandleEvents();
}
delete this;
}
void GameStateManager::HandleEvents(void)
{
// Respond to events
SDL_Event event;
while(SDL_PollEvent(&event))
{
if (event.type == SDL_QUIT) {
m_running = false; // Quit
}
else
{
int size = m_eventHandlers.size();
printf("Whooo! Size: %d\n", size);
for (EventHandler* handler : m_eventHandlers)
handler->OnEvent(event);
}
}
}