Steps to reproduce:
1. Start a new game.
2. Click somewhere in the visible area.
3. A dialog will pop up and the cursor will be moved to the center of the screen. Close this again.
4. (If necessary scroll over to some section of the map where you can see the black fog of war). Click on the fog of war.
Expected result:
Nothing happens, since the area is unknown.
Actual result:
The dialog is briefly shown as when clicking on a visible piece of land. Then, the game seem to remember this is fog of war and no dialog should be shown, so it is closed. For a player it will look like the dialog flickered and the cursor have been moved to the center of the screen.
In build16, nothing happens when clicking on the fog of war so something has obviously changed since then. I prefer this behaviour, since a player cannot do anything with the fog of war, so displaying the dialog makes no sense. (The lack of feedback is a better form of feedback here :p )
Just to rule it out, I tried with both sdl and opengl rendering and they have the same behaviour.
Widelands bzr r5991 on Ubuntu 11.04.
Did you build in debug mode? I can confirm the bug for debug mode in build16 and in rev5996. However, in release mode it is nether in build16 nor in rev5996. I'm on Win7 64bit, so might be different on Ubuntu, but I don't think so.
I'd suggest "Won't fix" if I'm correct with my guess.