I do have this problem. I was also blaming it on a cheap keyboard. It doesn't happen all the time. but I have noticed a few times, when I hit the space it triggers the Alt Key for some reason. At first I thought I was touching the Alt Key. Then I caught it when I know I was only touching the space.
There has even been times my cursor appeared to be in twelve differnet places at once for a split second. Then I would have to find where my cursor stopped at.