Could you please explain in details the steps to reproduce this issue? If I understand correctly, you have two pages:
1. Parent page with a UserControl on it
2. Child page (subpage of Parent page) that is not a part of site navigation i.e. Show in navigation
is set to No
It is not quite clear if both parent and child pages contain the same UserControl or the testing scenario is different. Are you changing the source code of the control or its properties in edit mode of the page? In the first case, the change should be reflected on all pages containing the control and in the second scenario the change should be just in the corresponding page.
Thanks for your cooperation in advance.
the Telerik team