Describe the bug
Pressing the left or right arrow keys once in certain screens of singularity consistently moves left or right by two units instead of one. I first noticed this in the Research window and thought it might be deliberate. However it also happens when moving through a set of bases in one region (thus skipping every other base), which is very annoying.

Up and down arrow keys work fine, as do all of the other keyboard shortcuts I've used. It's just left and right arrow keys.

To Reproduce
Steps to reproduce the behavior:

1. Construct bases until you have exactly 4 bases - all in the same location
2. Note the order of the bases so you can tell which one is the next.
3. Open one base and click the left or right arrow key.
4. Notice that you moved to bases and that you will never get the bases that are 1 or 3 steps from your starting position with the left/right click. (You can sometimes also see that the base name changes twice with every click)

Expected behavior
That a single keypress would only move exactly one base in the base list or one step on the research sliders

Desktop (please complete the following information):
singularity 0.30-2
Ubuntu 10.04
python 2.65.0ubuntu1
pygame 1.9.1release-0ubuntu1
numpy 1:1.3.0:0-3build1

(I have also reproduced locally on my PC Linux with Python3.7 in the current master branch, so it is definitely still present)

Additional context
I found this bug on Launchpad and imported it here. Link to LP#531871

Thanks to rww for reporting this bug.