User Control problem when > 1 on same form

Hi,

I have created a user control which contains another user control (in same source). The inner control is a numeric text box. The outer control is a container for 3 numeric controls - X,Y and Z by default.

Here is my problem. When the control first loads, if you change the value in the Y or Z field, it actually appears in the X field. Once you type in the X field, you can do what you like in any of them and it works. I cannot for the life of me work out why this is!
I apologise for the rough coding, but it's been a while since I did any VB or object-oriented class stuff.

The control and source code is attached. I hope this is an obvious newbie mistake that someone can point out to me. Thanks in advance for any help.

looking at the issue with fresh eyes this morning, I'm actually more confused. It should only be the inner control's code that is running, so why it would impact on other controls in the outer container I really don't know.