Not sure how your page is structured, but I would guess that you need to refresh the “actievePeriodehelper” to refresh the rest of the page (under the assumption that you display the period in a nested dataview over assocation). Generally, when refreshing an object, nested dataviews within that ‘object view’ are also refreshed.
Not sure what went wrong (and if it might in future still).
I have the refresh on the “ActievePeriodeHelper” already and it is a nested dataview in “Opleiding” which is the main entity.
At the moment I didn't change anything as far as i know, but it's refreshing atm again (I kept on coding the page further). So it's either something in my code above or something with my internetbrowser.
above of the Refresh in client their is a option “Commit” and then select yes(as by default it is no) radiobutton as it will save your changes.