Button state on aspx page affected by activity within ascx control?

[KatB]

Not sure I can even word this clearly, but...

I have an aspx page on which I have several tabs (button controls). Each
button causes the panel with a certain ascx control to become visible.

When I click on a tab (making it "active" to the user), I set the button
image using javascript. All is fine until I click on any postback
control within the ascx control. Then the button reverts back to its
original image/color. If I mouseover it, it returns to the correct "in
use" image (not the mouseover image).

Is there any way to effect a mouseover on the aspx page via code from
the ascx control?

Thanks, Kat