Wrong sprint when adding cards in Agile Board view

When I add a card in a sprint by using the plus in a swimminglane, i fill in a summary and description.
Next I double click on the new card to change the assignee and sometimes some other stuff
The problem is that the current sprint in this view is  changed to "Unscheduled". So when i close the item, the item suddenly disapears in the agile board. I can find the issue back at the unscheduled board.