windows - Weird repeat rate problem with new USB keyboard

I ran into a very weird repeat rate problem with my new USB keyboard.

I've always had PS/2 keyboards in the past, but the new computer I bought has no PS/2 input, so I had to get a USB keyboard (it's a "HP USB standard keyboard").

Anyway, my problem is that the keyboard doesn't respect the repeat rate I set in the Control Panel (I have Windows XP SP3 by the way). I set it to the maximum, but it really feels slower than it was with my old PS/2 keyboard. In fact, I ran a little test by keeping a key pressed in an editor for one minute and counting the number of repeated characters I get. With my old keyboard I get around 30 chars/sec (which is expected for PS/2), but with my new one, only about 20.

I've tried so many "tips" I found on Google or elsewhere to get the maximum repeat rate, but nothing seems to work. I've also tried Microsoft's FilterKeys, but the repeat rate seems very inconsistent.

But here's where it gets really weird: lately I noticed that when I start HeidiSQL (no idea why!), the repeat rate suddenly goes up and reaches the expected 30 cps. And that's globally, not just in HeidiSQL. But as soon as I close the program, the rate goes back to 20!

Maybe HeidiSQL does some strange initialization with the keyboard or something like that. But it shows that there is a way to set the speed up to 30 cps with my current keyboard. It just doesn't work if I do it via the Control Panel.

Any idea how I could get the maximum repeat rate of my USB keyboard without resorting to leaving HeidiSQL running all the time?