### Steps to reproduce

1. Go to the work package meetings tab

2. Start adding the WP to a meeting

3. Select an occurrence of a meeting series from the autocompleter and submit the form, adding the WP to the series backlog


### What is the buggy behavior?

* Trying to do the above steps again results in the occurrence still being visible

* Other occurrences are also visible, but adding the WP to any of them would also re-add it to the same series backlog


### What is the expected behavior?

* Adding to a meeting occurrence (of a series) adds it to the meeting agenda itself (as the last item), not the backlog

* For one-time meetings, Begin of the insertionit is nevertheless addedEnd of the insertion Begin of the deletion Parimal will get backEnd of the deletion to Begin of the insertionthe backlog


_**Note:** the process of selecting meetings and selecting whether a work pacakge should go to the agenda or the backlog will be improved with: <mention class="mention" data-id="62265" data-type="work_package" data-text="##62265">##62265</mention>_End of the insertion Begin of the deletion thisEnd of the deletion