条件为false，但if语句中的代码已执行

我有以下方法：

public bool ConnectAsync()
{
    if (IsConnected)
        throw new InvalidOperationException("Socket is already connected");

    if (IsConnecting)
    {
        throw new InvalidOperationException("Attempt to connect in progress");
    }

    . . .
}

其中：

    private readonly object padLock = new object();

    private bool isConnecting = false;

    public bool IsConnected
    {
        get
        {
            lock (padLock)
            { return socket.Connected; }
        }
    }

    public bool IsConnecting
    {
        get
        {
            lock (padLock)
            { return isConnecting; }
        }

        private set
        {
            lock (padLock)
            { isConnecting = value; }
        }
    }

如果我的变量isConnecting为false，为什么会执行if语句中的代码？

Why the code inside the if statement is executed if my variable isConnecting is false?

编辑：

如果我使用提交的 isConnecting 而不是属性 IsConnecting 我有相同的行为。代码在任何地方都在同一个线程中运行。

Edit:
If I use the filed isConnecting instead of the property IsConnecting I have the same behavior. The code runs in the same thread anywhere.

编辑2 ：

最后这是有效的：

lock (padLock)
{
    if (IsConnecting)
        throw new InvalidOperationException("Attempt to connect in progress");
}

这样做有效：

{
    if (IsConnecting)
        throw new InvalidOperationException("Attempt to connect in progress");
}

但为什么？