That's not a bizarre behaviour... Unity will serialize all public variables of your scripts so you can edit the values in the inspector. If you don't want the variable to be serialized, use the NonSerialized attribute.

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You can simply reset your instance by right-clicking at the components header and select Reset. This will erase all serialized data and re initialize the component. If your script has a Reset function, it will be called in this case. Reset is also called for newly added components.

Generally there are 4 types of variables (i've omitted static and protected):

Serialized variables:

public var var1 : String = "text1";  // the public keyword can be omitted in UnityScript

@System.SerializeField
private var var2 : String = "text2";

Non serialized variables:

@System.NonSerialized
public var var3 : String = "text1";  // the public keyword can be omitted in UnityScript

private var var4 : String = "text2";

The confusing thing is maybe that Unity automatically serializes public variables.

Another way is to initialize your variables in Start(). Start is called after the component has been initialized.

public var var5 : String;

function Start()
{
    var5 = "text5";
}

Here're the same examples in C#

Serialized variables:

public string var1 = "text1";

[System.SerializeField]
private string var2 = "text2";  // the private keyword can be omitted in C#

Non serialized variables:

[System.NonSerialized]
public string var1 = "text1";

private string var2 = "text2";  // the private keyword can be omitted in C#


public string var5;

void Start()
{
    var5 = "text5";
}

The variable is already defined and Unity will for some reason not save changes to the variable when the variable is edited in script.(I hope that sentence made sense). If you want to change it you cant do it in the script, you would have to do it in the inspector.