try to create a new control element for the tab control in your sub vi:
Move to the front panel of the sub vi and select "Element->Modern->refnum->element(refnum)" and place it on the frontpanel
right click this element and select "choose VI Server Class" (or similar, i'm using the german version) "general probes->G-Object->control element->tab control-> tab control"
This should work with any new tab control connected.
I assume you created your refnum control by copying it - then it was bound to the original tab control.
Thankyou Rich for your superlative support.
I was unaware that the datatype returned from a Tab Control was an enumeration that was formed by the names of the pages. In order to utilize the 'Value' property to manipulate Tab Controls that would have different page names I had to handle the Tab Control as unstrictly typed, which would return a Variant. By casting this variant to a I32 this would give the page number from the order they appear on the control and would not depend on the enumeration created by chaning the page names.