Webspace links
Sounds to me like you've been fully migrated to Greenby and the live data is now being hosted by Greenby servers and not PN servers.
Just my immediate thoughts below. May or may not be useful. I hope it makes some kinda sense and is of some help to you:
homepages.plus.net/username/something.htm will always display whatever is on the Ye Olde PN servers regardless of whatever the Greenby proxy is set to use.
www.username.plus.com/something.htm will always display whatever is on the LIVE server as defined by whatever the Greenby proxy is set to use. This could be a PN server or a Greenby server.
I have various old F9 and PN A/Cs with email and webspace. Even those which have allegedly been fully migrated to Greenby don't always have the data hosted by Greenby yet. Some migrated A/Cs are still being hosted by PN, some migrated A/Cs are actually being hosted by Greenby. It's a complete dog's dinner in every single respect 
You can kinda check the situation via ftp:
ftp to "homepages.plus.net" will always be Ye Olde PN server with a typ IP 212.159.8.91 and should announce itself as "plus.net ftp server #1" or similar during login.
ftp to "ftp.plus.net" may be Ye Olde PN server or a shiny new Greenby server as defined by whatever the Greenby proxy is set to use BUT it should always be the LIVE server.
The fundamental problem here is that ...
homepages.plus.net/username/something.htm
... will only work reliably (if at all) until Greenby finally takes full control of hosting and is actually hosting the live site data. Once that happens you will always need to be using the 'normal' URLs ...
www.username.plus.com/something.htm
... because at some point in time when everyone is finally migrated, PN will simply unplug homepages then it will be consigned to a recycling skip or whatever and gone for ever.
Try uploading some test files via ftp just to confirm which server is actually hosting the live data. Then you can specify your URLs accordingly. HOWEVER, I would stgrongly suggest that you avoid using homepages.* URLs if at all possible because I have no doubt that homepages WILL cease to exist eventually. I presume that you're using these URLs in order to serve https pages, yes ?
If so then I'm sorry to say that I think everything is going to go somewhat titsup for you once Greenby are hosting the data because I don't see any functioning https service whatsoever via Greenby only http. That doesn't bother me particularly but obviously it might be an issue for you. It's yet another awesome baked-in PN/Greenby bonus feature on this shiny new all improved system for us alleged 'valued customers' I'm afraid. I may be wrong. Things may change in time. But my money would be on it always being the biggest pile of excrement you could possibly imagine 
