index() referencing a repeat within a case that has not become toggled causes link-exception

I saw recently that formsplayer has defered initialization of cases until first use.
I have a repeat inside a case called rpt-transaction-profiles
I also have a binding that uses the function index('rpt-transaction-profiles') in the calculate attribute
I get an error after loading when I click on any tab (xpath syntax error ...)
I have found a workaround but was wondering if this is expected behavior?