(Hi James, lets see if I can remember this...)
Steps to reproduce Homepage problem:
1. enter url sans "http://" in Homepage field
2. hit [preview]
3. get told off for not having "http://" prefix
4. put in http prefix, hit [preview]
5. get told off for not having "http://" prefix
repeat 4..5 til you get annoyed
6. blank/clear Homepage field
7. hit [preview]
8. Look at your comment.
9. enter url WITH "http://" in Homepage field
10. hit [preview]
11. All good... hit [Post comment]

hth. no need to post this ;)