I found a bug that freezes FreeMind 1.0.0-RC4 on OS X, and I was able to reproduce the problem once. The way you do it is you copy a URL, the one I was using at the time was this:
Then you highlight a node, and hit command V to copy the URL as a child of that node. (Do not first create an empty child node and edit it, that will not trigger the bug.)
Once you've created that child node with the URL as described, now try clicking that node. It should open the link automatically in a browser. Now try deleting the node with the URL in it. When you do so the keyboard will no longer work to scroll between nodes, create new child nodes, etc.
Closing FreeMind and then reopening fixes the problem. I did not seem to have any data loss/corruption. I was able to reproduce this once, but it doesn't seem to be working a second time.