Traceback while navigating through debugger UI

I was using the arrow keys to navigate around the UI and suddenly the debugger crashed, the program I was debugging along with it, and this traceback showed up.

I've scrubbed the traceback a bit so it only shows relevant information:

```
Traceback (most recent call last):
File "..../python2.7/bdb.py", line 49, in trace_dispatch
return self.dispatch_line(frame)
File "..../pudb/debugger.py", line 210, in dispatch_line
self.user_line(frame)
File "..../pudb/debugger.py", line 431, in user_line
self.interaction(frame)
File "..../pudb/debugger.py", line 399, in interaction
show_exc_dialog=show_exc_dialog)
File "..../pudb/debugger.py", line 2236, in call_with_ui
return f(*args, **kwargs)
File "..../pudb/debugger.py", line 2497, in interaction
self.event_loop()
File "..../pudb/debugger.py", line 2463, in event_loop
toplevel.keypress(self.size, k)
File "..../pudb/ui_tools.py", line 120, in keypress
result = self._w.keypress(size, key)
File "..../python2.7/site-packages/urwid/container.py", line 1131, in keypress
return self.body.keypress( (maxcol, remaining), key )
File "..../python2.7/site-packages/urwid/container.py", line 2310, in keypress
key = w.keypress((mc,) + size[1:], key)
File "..../python2.7/site-packages/urwid/container.py", line 1621, in keypress
key = self.focus.keypress(tsize, key)
File "..../pudb/ui_tools.py", line 120, in keypress
result = self._w.keypress(size, key)
File "..../python2.7/site-packages/urwid/container.py", line 1621, in keypress
key = self.focus.keypress(tsize, key)
File "..../python2.7/site-packages/urwid/listbox.py", line 966, in keypress
return actual_key(self._keypress_up((maxcol, maxrow)))
File "..../python2.7/site-packages/urwid/listbox.py", line 1033, in _keypress_up
row_offset, 'below')
File "..../python2.7/site-packages/urwid/listbox.py", line 849, in change_focus
raise ListBoxError("Invalid offset_inset: %s, only %s rows in target!" %(offset_inset, tgt_rows))
ListBoxError: Invalid offset_inset: -4, only 4 rows in target!
```

Possibly relevant: I had the setting enabled where the terminal is hidden when not in use.