Here is a workaround that appears to cure the clipping.
box = wx.StaticBoxSizer(wx.StaticBox(panel, -1, field.Name),
wx.HORIZONTAL)
minw,minh = box.GetStaticBox().GetTextExtent(field.Name)
box.SetMinSize((minw+20, minh))
gui = field.Gui(panel, UI)
box.Add(gui)
gb