I've changed the [reply], [quote], [code], and [pre] tags on this forum by adding a
at the end of the closing tag html (Admin -> Markup -> Tags -> Modify) - that appears to solve the problem (but give it a try here and confirm).

As for spacing being not completely exact, this is an unfortunate result of limitations of how the editing components being used differ in some ways from the final HTML produced by GForum; since straight HTML is not allowed (for various security reasons), the resulting HTML has to be converted to markup, which is safe, then converted back to HTML when displayed. This does mean some content can be lost - for example, if you were to copy and paste a table from one page into the editor, the table would not be preserved because there are no table elements available in markup. That said, we do try to keep the final display as close as possible to the input when using functionality directly available in the editor, and if there is an area where the final result varies greatly, we can look into possible fixes for it.