I don't think it would make sense to delete all notifications for the focused application. For example, if I focus the window for one IM buddy, I don't want to see any more notifications of what that buddy said; but that has nothing to do with whether I want to see notifications for other buddies who are messaging me at the same time.
If a program is sending too many notifications, that's a bug in the program and should be reported against the program -- in this case, pidgin-libnotify. Reporting it against Notify OSD is like reporting a bug against Metacity complaining that an application opened 200 windows, or reporting a bug against GTK complaining that an application menu has too many items in it.
I don't think it would make sense to delete all notifications for the focused application. For example, if I focus the window for one IM buddy, I don't want to see any more notifications of what that buddy said; but that has nothing to do with whether I want to see notifications for other buddies who are messaging me at the same time.
If a program is sending too many notifications, that's a bug in the program and should be reported against the program -- in this case, pidgin-libnotify. Reporting it against Notify OSD is like reporting a bug against Metacity complaining that an application opened 200 windows, or reporting a bug against GTK complaining that an application menu has too many items in it.