When I log in to my Windows laptop via iPad, it works fine, but my laptop screen resolution changes from 1440*900 to 800*600.

It reverts back when I close the Splashtop service in laptop.

Is there any way to prevent it changing the laptop screen resolution?

From the list of computers, click the blue arrow button next to your laptop. That will take you to the Computer Settings screen. From there click "Advanced" and under the Resolution setting choose "Use remote computer's native setting."

I really wish Splashtop would use this as the default setting. I don't mind the resize while streaming, but moving everything around on the host after the fact is really a pain.

Yes that worked but it left lower bit of iPad screen blank

Your iPad and pc have a different resolution, one of them has to change when you connect using splashtop, so one if them isn't going to display ideally on it's native screen.