I'll describe the scenario with an example.

1) I have a screen -> "Screen A".
2) I've create a UberfireDock -> "Dock A" that holds "Screen A"

When I go to the given dock button for "Dock A", then the Dock is opened and the @OnFocus method of "Screen A" is executed. This is fine, since the screen was just opened.

Now if for example "Screen A" has a button, and I click on this button, the @OnFocus method of "Screen A" is executed again.
But the "Screen A" already had the focus, since it was just opened.
If we click in whatever any other UI component of "Screen A", the @OnFocus method is invocked over and over again.
This behaviour in some way breaks the semantic of the @OnFocus, but also can be werid given that some docks needs to be aware of he on focus event in order to refresh the UI, etc.