if you place the control in a repeating table, the control gets created
multiple times with the same id/name. In infopath you should always
think of controls as nodes in xml.

So, when controls are placed in repeating table, each control is
analogous to nodelist in the underneath xml.

each control acts as a different control and all the rules on the on
each controls are applied to the control itself and not to other
controls.

Now if you want to know what control was changed, you can use VSTO to
write simple code to check the changed node in the nodelist.