In lvl1 I had the same problem only with 4 planets!! I took multiple screen shots and over layed them in photoshop (sorry about the resulting shading);

There are 4 planets I can't get to; Top-center, two in the left middle, and one bottom center.
Here's the worst part though. After I had secured all available planets and found these 4 unreachable I got attacked by enemy forces (as you can see in the screen shot)! Does this mean that the computer isn't limited to the same parameters as the player?!?!
Honestly I love the game though! Everything has bugs. Keep up the great work guys.