>If this is PROVEN to have happened directly/shortly after user input, check if somehow biz logic blocks deletion of previously selected item or tries to set additional item automatically. If uncertain, prove first that you did not somehow try to set selected=true to more than 1 item via SQL or biz code

This confirms I have resolved the issue.

This was when the user tried to access a form where two selected=true was being done. This was a side effect of an adjustment needed in a merge process. Duplicate records were created. And, on those duplicates, one was at least applicable to selected=true.

Thanks