Windows XP Professional, SP2, Nvidia GeForce? 8500GT at 2560x1024
Just upgraded to a dual monitor setup. Started 3.0.9, enlarged the main window to take most of the screen (minus monster list window and Windows taskbar on right side) and opened a saved game. Saw error message "screen width too small" error, and the game died. Started Angband again, loaded up the saved game, and then enlarged the main window. At a certain point, after the full dungeon can be seen, the display suddenly resets to only show the first 15 characters on the left side. I can't tell how much it is in characters, but it looks like it happens roughly at the 2000 pixel size. After shrinking the screen below that point, it displays properly again.
Angband actually sees the screen at 15 characters - I cast a spell, and all the messages were chopped off at 15 characters, so I had to hit "space" multiple times.