As I was making this module (http://www.adventuregamestudio.co.uk/yabb/index.php?topic=36228.0),
I've encountered a little bug.
It seems, that the special dialog surface has a problem with transparent areas.
(http://blog.sonores.de/wp-content/uploads/2008/12/customdialog_bug1.png)
The text is fine on the disc, but messed up on the transparent side.
But I can wipe away the garbagepixels with the cursor :)
Are you doing a Surface.Clear call in your dialog_options_render function?
I've tried that too, using a surface.clear(COLOR_TRANSPARENT) gives me the same result.
But the screenshot is from using surface.DrawImage
I'll see if I can reproduce this, however I'm quite busy at the moment so I'll try and look into it later in the week.
Sure,
I'm not in a hurry.
Who's not busy at the end of december ;)
Sorry it took a while, but I have now verified this as a bug in AGS, and I'll get it fixed for 3.1.2.
:)