Two issues at play here.
One is there was a bug in our udisks script that was preventing the correct access permissions being added to the automounter shares under some conditions - the symptoms are username/password refused for the automount shares but the osmc share would work.
I’ve fixed this last night so please run updates to get that fix.
The second issue is a bug in later versions of OS X that use SMB3 which causes exactly what you describe. I know for sure that Mavericks has this problem and Snow Leopard does not, so it occurred somewhere between those two versions.
The solution is not to try to open the shares while you’re still connected as Guest - click the Connect as button in the top right and sign in as osmc/osmc for username/password, and check the box to save these.
Once you do that you should find you can access the shares. In future if you ever find yourself browsing the share list as guest make sure you use connect as before going into a share. (Shouldn’t be necessary though if you save the password)