Yeah, this behaviour's been bugging me for awhile, so I had a look at it. The problem is that the regular expression that that's used to get the ID of the item you're highlighting doesn't understand the IDs given to new pages before they're saved.
A regular ID looks like "record-1" (which is the homepage), but a newly created page has an ID like "record-new-Page-0-1" which is the first - number 1 - new page in the page root (which has an ID of 0).
What the regex does is take everything after the final "-" in the ID, which ends up with "1" for both the examples above, hence the problem.
Now I'm no regex expert, so this probably isn't the best way but it seems to fix the problem if you go into /jsparty/tree/tree.js, and change about line 497 from
if(this.id.match(/-([^-]+)$/)) return RegExp.$1;
if(this.id.match(/([^-]+)-(.+)$/)) return RegExp.$2;
What this does is get everything after the FIRST "-" instead of the last one, so the homepage above will still return "1", but the new page will return "new-Page-0-1", which is what we want.
Then again there might be a reason why it works like it does...