After following the instructions on manual screen shooting of the page
Here are some issues I found.
1) The code snippet suggested at the bottom of the dialog miss double quotes in tags attributes. The image in the wiki page clearly shows it.
Attributes with no quotes:
2) on saving the dialog image, the suggested filename is not the dialog outer widget title, but the dialog .ui file name.
example: when saving 'Pick a Color' dialog, the suggested filename is "colorpickerdialog.png" instead of "ColorPicker.png". The last is what the code snippet suggest.
3) the <alt> value could be the dialog title (e.g. "Pick a Color")
4) same for the <caption> tag, that is not suggested in the snippet, but is valid for XHP.
I trust you :D