AF modes and Canon IS Lens

In the owner's manual, AI Focus should be selected over One Shot or AI Servo in case the subject starts to move, and if it was a moving subject, then AI Servo should be selected.
Now, I tried having a friend of mine stand still, put the camera in AI Focus, then had him move just before I pressed the shutter button, and he came out all blurred out.
However, I repeated the same procedure, but with the IS turned OFF, and he was in focus, with no problems. I used my 28-135mm IS for this test.
Now, doesn't that mean that either AI Focus or IS is completely useless? Well one negates the other!
It's even worse on the 75-300mm IS lens: AI focus is exactly the same as One Shot. I also think that keeping the focus on AI servo all the time produces noisier shots.
Would anybody please explain?
Please note that I tried more shots, at various focal lengths, just to be sure, and I always had similar results to the first test.

It is only refocusing when you have the shutter release button held in half way. Could this be the problem,.. or am I assuming wrong.

Well here goes the sequence:
1-Focus set to AI Focus, IS is on.
2-Subject is standing still, then I press shutter button 1/2 way in.
3-Subject starts moving as I completely press in the button.
4-Blurry picture.

Now with the IS set to off, the picture doesn't come out blurry.
Or, if the Focus is set to AI Servo, and IS is ON, the picture also is not blurry.
So what is the circumstance for using AI focus instead of One Shot or AI Servo, with an IS equipped lens?

It would seem to me (and I could be totally wrong on this) that IS is used to steady an image that would otherwise be blurred by the movement of the camera. It shouldn't be affected by the subject moving. The subject can jump up and down all he wants and IS shouldn't give a hoot.

AI Focus and AI Servo, on the other hand, would try to keep the subject in focus if the subject moved away or towards the camera.

I would therefore think that IS and AI focusing would be independent of each other. But you do present an interesting case and I have no idea why you're getting the results you're getting.

I think the IS takes around 0.5 sec to kick in after you have pressed the shutter, so that may be the cause of your problem.

Regards,

Is there a sleep time for the IS Gyro,. or does it switch itself off directly after a shot?

I also failed to realise that you were in AI Foucs asopposed to Servo... AI Foucs is quirky,. as it "Decides" seemingky randomly when to switch to AI servo type full time and when not.

For that reason when I am concerned about keeping focused on a moving subject,. I use AI Servo.

One last question. Do you have only one focus point selected?

I don't know about the sleep time for the IS, and yes, I have one focus point selected. I will test tomorrow with multiple focus points..

The IS kicks in as soon as you press the shutter button although, as Roger said, it may take a split second to stabilize. However, it DOES stay on for as long as you have the shutter pressed and only goes off a split second after you release the shutter. If you were to look at your battery meter instead of your viewfinder, I bet can actually see the battery meter dropping as the IS sucks up all your battery juice while you keep the shutter depressed, even half-way!