I think this might be a server-side issue more than a bug, but on both an Ubuntu 10.04 installation and an Ubuntu 12.04 installation (the current one) when trying to use the Ajax FTP service, uploads cannot be performed.
It gives a 413 error and says something about "cannot create temporary copy to save on the server". That's not exact words, but it's close enough.
This is version 1.1.0-beta1
Is this a server problem like I expect? And if so, how can I fix it?