Here's some of the bugs that I've found while using external windows. Keep in mind that I am on Windows so these bugs might not all be true for Mac or Linux users.
- GuiShowImg Polygons - These don't work. When you set the polygon variable, the gui object just doesn't display anything. I tried this with both textured (with an image) polygons as well as single color polygons. Drawing of lines (size 4 array) doesn't work either.
- Gui Alpha - I've noticed some of the Gui object types are not effected by their alpha variables. Most notably are GuiDrawingPanels. I've also seen this on GuiButtonCtrls but haven't tested it on any others.