In some applications (such as PaintShop Pro 6, WordPad on Windows Me/2000, etc.), when superscript or subscript vowels or tone marks are typed, they force a space to appear before the following character.  This is due to a problem with the RichText control that is supplied with Windows. Although a modification to the older Lao fonts sometimes avoided the problem, that modification is not possible with Lao Unicode fonts, and until Microsoft correct the part of Windows that causes the problem, there is probably no really satisfactory solution, other than avoiding the use of those applications.