The file dialog always starts from the directory of your most recent file.
You should be able to access your sd card by using the "up" button in the file dialog until you reach the top level, where it usually displays your internal partition and your sd card. There is however one exception: if you open a file on another (not MyDocs or SD Card) partition (e.g. inside /tmp in connection with browser/e-mail and dbus-switchboard) you only get to the top directory of that partition. One easy workaraound for this is keeping a pdf file on your sd card in the "recent documents" list. First load this file and then click open.
Edit: Additionnaly, you can, of course, access any file via console: "flatboat /path/to/my/file".

The icon means "save" and is greyed out, because you didn't modify the document. It's just a modern replacement for the standard floppy icon and does not represent the place you save to.

I already found some new bugs and I will als look into the file dialog for the next bugfix release, but this may take a week or two, since I'm quite busy at the moment.