When adding a forum, the categories are not ordereb by the order number, but rather by name.

Replace:
SELECT Cat_Title,Cat_Entry FROM {$config['tbprefix']}Category WHERE Cat_Type='forum' ORDER BY Cat_Title


With:
SELECT Cat_Title,Cat_Entry FROM {$config['tbprefix']}Category WHERE Cat_Type='forum' ORDER BY Cat_Number

Thanks. I've filed an internal bug on this.

This one is fixed in 6.5.3

If we are going to shake CP, then I noticed some weird behaviour in 6.5.2 when changing names of the forums. I would click save and the page would load back intact. So I had to change the order of the forums as well for the new name to actually save and then change the order back. It was happening under certain combination only, I think, so I don't know if it is even a bug.