Web User Control problem.

[CM]

Hi there:
I created two web user control A and B.
If I put A and B on the same web page, something strange happened:
1) The control A would not respond to button click event if it is put behind
control B. It respond to click event only if it is put at a place before or
above B.
2) All link on B will respond click event, but a button on B didn't respond
any click event, no matter it is put, before or after A, above or below A.
What could be the reason?
Any help would be appreciated!
CM