it shouldn't require changing or adding jvm options for it to work... hmm...
which build are you on exactly? 659? (click the Help --> About to see which build you are on)
Are you using the embedded java version or the "online" installer? Or your own system java?
I'm running 659 on my office machine and am not experiencing this issue, but i'm also not using LDAP auth, so our usage scenario is different.
Maybe try logging into the igniterealtime.org openfire server with your spark and see if the issue presists?
You can create a new account through spark by logging out of spark (so you are on the login window) --> Accounts --> fill in a username and password. server is "xmpp.igniterealtime.org" --> Create account --> Login