Replacement GoToolManager not active before click?

I have replaced GoToolManager with my derived version supporting mouse and keyboard input. Everything works, but I have noticed that I must click the diagram in order to make my ZoomingToolManager working.

When I run my application neither rotating mouse wheel nor pressing keys doesn’t fire ZoomingToolManager’s event handlers. It doesn’t mean that the diagram is not receiving any input - mouse wheel scrolls the diagram up and down, so the default GoToolManager must be handling this event. After clicking anywhere inside the diagram, mouse wheel performs zooming - ZoomingToolManager is active.
I have version for WinForms.

Any suggestions?

When you initialized your GoView, did you set both GoView.DefaultTool and GoView.Tool to an instance of your replacement tool/manager?

The following code is in the constructor of a control hosting GoView:

//zooming replacement for ToolManager
ZoomingToolManager zoomingToolManager = new ZoomingToolManager(diagram);
diagram.DefaultTool = zoomingToolManager;
diagram.ReplaceMouseTool(typeof(GoToolManager), zoomingToolManager);

GoView.DefaultTool specifies the tool to use when the current tool stops running.
GoView.Tool indicates the currently running tool. Since you haven't set that, that is why your custom tool isn't running until after you click on the view. The click probably invokes the GoToolSelecting tool, after which it finishes and sets GoView.Tool = GoView.DefaultTool. At which point your custom tool is running....
Calling GoView.ReplaceMouseTool(typeof(GoToolManager), ...) doesn't do anything, since initially there is no instance of a GoToolManager installed as one of the mouse tools (i.e. mode-less tools). It's GoToolManager's job to choose one of the mouse tools and make it the current/running tool. It wouldn't make sense for a GoToolManager to select another GoToolManager to actually do any work.

Thanks Walter, it works.
Adding one line solved the problem:

diagram.Tool = diagram.DefaultTool;