In Custom Editor, After Event.Use(), how to get state of mouse input ?

Hello, I am doing a simple Resizing function in an editorWindow:

Code (CSharp):

1. if (Event.current.type == EventType.MouseDown)
2. {
3.      isResizing = true;
4. }
5. if (isResizing && Event.current.type == EventType.MouseDrag)
6. {
7.         //
8. }
9. if (isResizing && Event.current.type == EventType.MouseUp)
10. {
11.          isResizing = false;
12. }

It works well, except one bug:
If I start to resize, and then, when I am still holding, I leave the editorWindow with my mouse, if I release the button, nothing happen.

But when I come back to my editorWindow with my mouse: the code is still at isResizing = true

How can I resolve this little bug ?

Thanks !