I've found a bug when using a nested grid editor within a grid that uses triggerEvent: 'singletap'. The child cells cannot be edited on the first try. Then if the child cells are successfully edited, the parent grid cells can no longer be edited.

To reproduce, open the fiddle (https://fiddle.sencha.com/#view/editor&fiddle/33id) and then:
  1. Select an option from the combobox in the "Shoe" column, which will populate the nested grid.
  2. Click on the "Condition" value in one of the nested rows. This activates an editor with an empty value instead of the existing value.
    1. By clicking on the "Condition" value of the other nested row, the expected value is kept in the editor, and now either row can be successfully edited.
    2. But after editing a child cell, any attempt to edit a cell in the parent grid is unsuccessfully, throwing an error message "TypeError: activeEditor.$activeLocation is null"

  3. After activating the nested cell editor the first time (and before getting to the point of activating it successfully), if you instead lose focus by clicking outside the parent grid, further attempts to activate the nested cell editors will also throw the same error message "TypeError: activeEditor.$activeLocation is null"