yii2-grid EditableColumn invalid ajax url only for the element of the first row and first column

Question

I find a very strange problem using the yii2-grid by kartik. When I use the EditableColumn plugin and set the form action to a specific url, it seems to be working for all the elements of the grid except for the top left element, the one in the first row and first column.

My grid is very simple, it has 3 columns all of which need to use the editable column plugin. All other elements update correct. The problematic element seems to ignore the action paramter passed in the formOptions configuration parameter of the Editable Column plugin.

Has anyone else met this problem and managed to find the cause?