send("{CAPSLOCK ...}") doesn't always work

send("{CAPSLOCK on}")
send("{NUMLOCK on}")
send("{SCROLLLOCK on}")

I'm finding that the above code seems to work for the NUM and SCROLL locks, but not always for CAPS lock.  When I execute the code for CAPS, I see the CAPS light on the keyboard flash for a split second, then revert to previous state, whether I use ON, OFF or TOGGLE.

Is there any known cause for this activity?  As far as I can tell, there is no other software running that would trip the CAPS lock back.

If it makes a difference, I'm running Windows 7.