What's going on is that when the form is finalized, the choice list is recomputed for every select and values that are no longer available are cleared. By finalization time, the accumulator (previously_selected_strc in your case) includes every single selection ever made and so all answers are cleared.
It's possible that there's been a change of behavior here but I don't think so. When I've written this kind of form, I've always explicitly made sure the choice_filter includes the choice for the current repeat instance.
For example, this form has the following choice_filter:
name = current()/. or not(selected(join(" ", /select-no-duplicates/repeat/option), name))
I think you could add name = current()/. or to your existing condition to get the behavior you want.
Your form does point to a bug. When the value for a select is cleared because its choice no longer is available, any calculates that reference that value should be updated. Basically, your workaround is not supposed to work. 